Operator
I would now like to hand the conference over to your speaker today, Paretosh Misra. Please go ahead, sir.
Paretosh Misra
Good morning, everyone. I'm Paretosh Misra, Vice President of Investor Relations, and I'm joined this morning by John Lee, President and Chief Executive Officer, and Ram Mayampurath, Executive Vice President and Chief Financial Officer.
Yesterday, after market close, we released our financial results for the fourth quarter and full year 2025, which are posted to our investor website at investor.mks.com. As a reminder, various remarks about future expectations, plans, and prospects for MKS comprise forward-looking statements.
Actual results may differ materially as a result of various important factors, including those discussed in yesterday's press release and in our most recent annual report on Form 10-K and any subsequent quarterly report on Form 10-Q. These statements represent the company's expectations only as of today and should not be relied upon as representing the company's estimates or views as of any date subsequent to today, and the company disclaims any obligation to update these statements.
During the call, we will be discussing various non-GAAP financial measures. Unless otherwise noted, all income statement-related financial measures will be non-GAAP, other than revenue and gross margin.
Please refer to our press release and the presentation materials posted to the Investor Relations section of our website for information regarding our non-GAAP financial results and a reconciliation to our GAAP measures. Our investor website also provides a detailed breakout of revenues by end market and division.
Now, I'll turn the call over to John.
John Lee
Thanks, Paretosh, and good morning, everyone. 2025 was a year of impressive execution for MKS in a gradually improving demand environment.
Year over year, we delivered 10% sales growth, 20% EPS growth, and over 20% free cash flow growth. We maintained strong gross margins despite trade policy dynamics, while staying focused on delivering for our customers, investing in our business, and proactively bringing down our leverage.
We're proud of our accomplishments in 2025 and grateful for the continued support and collaboration of our customers, suppliers, and employees. Our partnerships and engagement have been critical as we work together to deliver the broadest portfolio of differentiated solutions that are foundational to advanced electronics in the AI era.
As we begin 2026, the demand outlook across our semiconductor and electronics and packaging markets is strengthening, and we are already seeing this in the ambitious capex plans announced by large chip manufacturers. MKS has a long track record of outperforming WFE in rising spending environments, and we are in an excellent position with our broad and deep portfolio of designed-in products that are foundational to semiconductor manufacturing and electronics and packaging.
I'll highlight some examples as I review our financial and end-market performance. Our Q4 revenue, gross margin, and earnings per diluted share all came in above the midpoint of the guidance ranges we provided on our Q3 call in November.
Revenue was strong across all three of our end markets. In our semiconductor market, revenue was above the high end of our guidance, driven primarily by subsystems serving etch and deposition applications in the DRAM and logic foundry markets.
Our plasma and reactive gases business delivered another strong quarter. We also maintained healthy momentum in dissolved gases for advanced logic applications and in back-end applications related to high-bandwidth memory.
Order activity in both areas remains robust. NAND-related activity remained stable sequentially, as expected.
I'm also pleased to note that our semiconductor business outperformed estimated WFE growth for the full year 2025, consistent with our track record of outperforming industry spending in improving demand environments. Looking to the first quarter, we expect semiconductor revenue to be up on a sequential basis.
We believe this outlook is consistent with market views of steady improvement in industry spending over the course of the year. With our global footprint, broad product portfolio, and deep technical expertise, we are ready to respond to demand as it comes, with solutions that solve our customers' hardest problems and enable their increasingly complex roadmaps.
On that front, we are excited to be ramping our new super center factory in Malaysia in the second half of this year, which will give us added capacity and resiliency to meet our customers' needs. Turning to electronics and packaging, revenue came in near the high end of our guidance.
The sequential increase was primarily driven by increased flexible PCB drilling and chemistry equipment sales. The flex market continues to largely follow seasonal patterns tied to smartphone and PC cycles, and we also saw continued momentum in orders for our chemistry and chemistry equipment solutions for advanced PCBs related to AI applications.
AI is driving increasing packaging complexity, and we are uniquely positioned to help our customers with the broadest portfolio of differentiated solutions. Excluding the impact of FX and palladium pass-through, chemistry sales increased 16% in the fourth quarter and 11% for the full year compared to the same periods in 2024, reflecting another year of healthy growth.
When we acquired Atotech in 2022, we saw the importance of advanced packaging for electronic devices well ahead of many in our industry. With AI now rapidly driving demand for more complex PCBs with rapidly increasing numbers of layers, we are seeing growth despite multi-year softness in smartphones and PCs.
Looking ahead to Q1 and the anticipated seasonal impact from the Lunar New Year holiday, we expect electronics and packaging revenue to be up slightly sequentially and to increase in the low 20% range year over year. Key drivers for our expected performance in Q1 include higher flexible PCB drilling revenue and a continued strong performance in our chemistry equipment business.
In our specialty industrial market, revenues came in at the high end of our guidance. We saw sequential improvement in research and defense and certain industrial applications.
Looking ahead to Q1, we expect specialty industrial revenue to decline low to mid-single digits, mainly due to the Lunar New Year holiday, which impacts our general metal finishing business. Year over year, we expect revenue to be up in the mid-single digits, led by the industrial and research and defense markets.
Overall, our specialty industrial market continues to deliver steady performance and contribute attractive cash flows. Our fourth quarter performance and outlook for Q1 underscore our strong position across our two key end markets.
In semi, we continue to strengthen our position in supporting leading-edge foundry and high-bandwidth memory investment through our vacuum and photonics offerings, while also remaining well-positioned to capitalize on large-scale investment in NAND equipment upgrades expected over the next several years. In electronics and packaging, we are demonstrating momentum with equipment and chemistries ideally suited to supporting smaller, more complex, and more vertical packaging structures for AI and other emerging devices such as foldable phones.
We expect this business to grow over time as we realize the long-term revenue streams from proprietary chemistries moving through production lines built with our equipment. The secular drivers powering our end markets are fully intact and present exciting opportunities for MKS in the years to come.
Our business is in a strong position with a resilient global footprint, margins that reflect the value we deliver, and strong free cash flows that we are reinvesting into the business and using to pay down debt. Lastly, we are proud to have been honored for the third consecutive year as one of America's Most Responsible Companies by Newsweek and Statista, an honor that reflects our continued focus and commitment to our people, customers, and suppliers.
Now, let me turn it over to Ram to run through the financial results and first quarter guidance in more detail. Ram?
Ram Mayampurath
Thank you, John, and good morning, everyone. We ended the year with a very strong fourth quarter.
Demand increased across all three end markets, we delivered healthy margins, robust free cash flow, and made meaningful progress on our deleveraging goals. That progress has continued into the new year, with another $100 million voluntary prepayment on our term loan in February, as well as further optimization of our capital structure with the recently completed issuance of $1 billion senior unsecured notes and the refinancing and extension of our term loan maturities.
I'll cover these topics in detail in my remarks. Let me start with the results for the fourth quarter.
MKS reported revenue of $1.03 billion, up 5% sequentially and 10% year over year. Fourth quarter semiconductor revenue was $435 million, up 5% sequentially and 9% year over year.
The result was driven by strengthening demand, especially in DRAM and logic and foundry applications. The sequential increase was led by plasma and reactive gases products.
Year-over-year comparison reflect more broad-based strength across many product categories, providing further evidence of an improving semi demand environment. Fourth quarter electronics and packaging revenue was $303 million, an increase of 5% quarter over quarter and 19% year over year.
The sequential improvement reflected higher flexible PCB drilling and chemistry equipment sales. The strong year-over-year comparison reflected healthy underlying growth across chemistry, flexible drilling equipment, and chemistry equipment.
Chemistry sales in the quarter were up 16% year over year, excluding the impact of FX and palladium pass-through, marking another strong year in chemistry revenue. In our specialty industrial market, fourth quarter revenue was $295 million, an increase of 4% sequentially, largely due to the improvement in our research and defense markets, as well as certain industrial applications.
This was partially offset by a decline in automotive. Revenue was up 5% on a year-over-year basis, supported by modest improvement across several of our key market categories.
However, automotive segment remained soft. Turning to gross margin, we reported fourth quarter gross margin of 46.4%, which was above the midpoint of our guidance.
While margins were down year over year, it was a very solid performance given ongoing impact from higher tariffs, higher palladium prices, which are passed through at zero margins, and the effect of higher chemistry equipment in our overall mix. Fourth quarter operating expenses were $263 million, slightly above the guidance range, primarily due to higher variable compensation due to stronger-than-expected results.
Fourth quarter operating income was approximately $217 million, yielding an operating margin of 21%, which was above our guidance midpoint. Fourth quarter adjusted EBITDA was $249 million, yielding 24.1% margins, and also above the midpoint of our guidance.
Net interest expense was $42 million. Fourth quarter effective tax rate was 1%, which was in line with our guidance.
We finished the year strong, with fourth quarter net earnings of $168 million, or $2.47 per diluted share, which was above the midpoint of our guidance. We closed the quarter with approximately $1.4 billion of liquidity, comprised of cash and cash equivalents of $675 million and our undrawn revolving credit facility of $675 million.
Net debt at year end was $3.6 billion. That, combined with improving adjusted EBITDA, resulted in a net leverage ratio of 3.7 times, based on full year 2025 adjusted EBITDA of $966 million.
Quickly summarizing our full year 2025 results: revenue was $3.9 billion, up 10% year over year. Semiconductor revenue totaled $1.7 billion, up a healthy 13% year over year, driven by plasma and reactive gases and vacuum products.
Our service business remained a steady and meaningful growth contributor. Electronics and packaging revenue was $1.1 billion in 2025, up a strong 20% year over year.
Total chemistry sales increased 11% year over year, excluding the impact of foreign exchange and palladium pass-through. Specialty industrial revenue was $1.1 billion, down 4% year over year, primarily driven by softness in industrial markets, including automotive.
Gross margin was 46.7%, down 90 basis points year over year, driven by additional costs related to tariffs and product mix, including record chemistry equipment sales. We moved quickly during the year to mitigate the impact of tariffs.
That impact was largely mitigated on a dollar-for-dollar basis by the fourth quarter, but will still continue to impact gross margin by about 50 basis points. Full year operating margin was 20.7%, down 60 basis points year over year as a result of lower gross margin.
However, our operating expenses as percentage of sales was 26% and improved by 30 basis points year over year. Let me now turn to cash flow and balance sheet discussion.
For 2025, we generated operating cash flow of $645 million, an improvement of $117 million year over year, even with an uptick in capital expenditures. Full year free cash flow was $497 million, an increase of 21% year over year and reflective of a very healthy conversion rate of our non-GAAP net earnings.
In 2025, we made a total of $400 million of voluntary prepayments on our term loan. This month, we made another voluntary prepayment of $100 million.
Since February 2024, we have paid down over $1 billion of our debt. We continue to remain focused on deleveraging.
We also closed a few key financing transactions in recent weeks. The repricing of our term loan facility reduced credit spreads on our US term loan by 25 basis points and the euro loan by 50 basis points.
In connection with the repricing, we increased the size of our revolver to $1 billion. Finally, our successful €1 billion bond offering has allowed us to diversify our capital structure, reduce interest rates on our debt, replace a portion of our secured debt with unsecured debt, and extend our maturities.
Based on current interest rates, the combined effect of these actions we took in this month will reduce annual interest expenses on a run-rate basis by approximately $27 million. In addition to lowering interest rates, these transactions will provide greater flexibility for the company.
Finally, during the quarter, we paid a dividend of 22 cents per share, or $15 million. As we announced last week, the board authorized a 14% increase in the next dividend, which is payable in early March.
Let me now turn to first quarter outlook. We expect revenue of $1.04 billion, plus or minus $40 million.
By end market, our first quarter outlook is as follows: revenue from semiconductor market is expected to be $450 million, plus or minus $15 million; revenue from electronics and packaging market is expected to be $305 million, plus or minus $15 million; and revenue from our specialty industrial market is expected to be $285 million, plus or minus $10 million. Based on anticipated revenue levels and product mix, including sequentially lower chemistry sales due to the Lunar New Year, we estimate first quarter gross margin of 46%, plus or minus 100 basis points.
We expect first quarter operating expenses of $270 million, plus or minus $5 million. Looking to the rest of the year, we will continue to invest in the growth of our business, but we expect operating expenses to grow at a rate slower than revenue.
We estimate first quarter adjusted EBITDA of $251 million, plus or minus $24 million. We expect capital expenditures to average in the 4% to 5% of revenue through 2026.
We expect a tax rate of approximately 21% in the first quarter. For the year, we expect our tax rate to be in the range of 18% to 20%.
Based on these assumptions, we expect first quarter net earnings per diluted share of $2.00, plus or minus 28 cents. Wrapping up, MKS continues to execute at a high level, meeting growing customer demand and maintaining strong profitability.
We continue to prioritize making the necessary investments in the business and proactive deleveraging. We believe that we are in an excellent position to capitalize on what we expect to be a robust demand environment.
With that, Operator, please open the call for questions.
Operator
Thank you. As a reminder, if you would like to ask a question, please press star one one on your telephone and wait for your name to be announced.
To withdraw your question, please press star one one again. We ask that you please limit yourself to one question and one follow-up before re-entering the queue.
One moment for our first question. Our first question comes from the line of Steve Barger with KeyBanc Capital Markets.
Your line is open, Steve. Please go ahead.
Steve Barger
Thank you. Good morning.
I wanted to start with the 46% gross margin midpoint guide. How much of that is from chemistry equipment mix, and does the lower 1Q sequentially suggest an upward inflection in 2Q from higher chemistry sales volume, or how do you expect that to play out as the year progresses?
Ram Mayampurath
Hi, Steve. This is Ram.
I'll take that. I'll start with your second question.
The answer is yes. It is due to the seasonality from lower chemistry driven by Lunar New Year, and we expect the mix to improve in Q2 and further in Q3.
Mix is the main reason for the 46% plus or minus 100 basis points guide.
Steve Barger
Got it. That should be the low point of the year.
Understood. John, can we just talk about the memory shortage?
It seems like that could be both good or bad for you. Can you talk about what you're seeing with NAND tool upgrades and other memory investments that could be coming, and then can you talk about what happens with consumer products, just given the increase that you're seeing in the market?
John Lee
Steve. Good morning.
I think the customers and our customers' customers are putting a lot of the investments in DRAM, obviously, for AI. That's causing this crunch in terms of availability of memory.
I would say this, the industry is moving very fast to try to meet those demands. You see a lot of announcements of fabs going up and what not.
Then more recently, NAND has become, potentially, a bottleneck as well in terms of availability. You saw one large chip company announce a new NAND factory, brand new greenfield, that's out a little ways, but that's good because it extends the ramp, if you will.
In terms of upgrades, I think our customers are best to answer that. I would say this: we have plenty of capacity to meet those upgrades should they come.
As a reminder, our position in RF power for NAND vertical channel hole etching allows us to enjoy upgrades almost as much as a greenfield. I think NAND is something that's going to be kind of icing on the cake as that happens throughout the year and the next couple years.
Steve Barger
Got it. Then just any comment on consumer products, what the potential effect could be?
John Lee
I think it's going to depend on how much availability there is. I think you read some analyst reports, people are kind of thinking maybe low single-digit decreases in PCs and in phones.
That really is going to be dynamic throughout the year. I think it's really going to be a function of how fast the industry can make those chips for that segment of the market.
I think if we have a little decrease in PCs and smartphones, I think it's going to be more than made up with AI.
Steve Barger
Got it. Thank you.
John Lee
Thanks, Steve.
Operator
Thank you, and one moment for our next question. Our next question will come from the line of Jim Ricchiuti with Needham & Company.
Your line is open. Please go ahead.
Jim Ricchiuti
Thank you. Good morning.
I'm wondering if we look at the electronics and packaging business, the 20% plus growth in 2025, John, any sense as to how much of that was a function of capacity additions, and yeah, I'm curious how much of a tailwind would you anticipate this being in 2026 in this area of the business?
John Lee
It's a good question, Jim. I think what we said also was that while the electronics and packaging grew 20%, chemistry grew about 11% year over year.
That's great growth, too. Chemistry would be more utilization-dependent, and then the rest of that growth is capacity additions from chemistry equipment, as well as flex drilling equipment.
We've talked about our chemistry equipment, that's a nice leading indicator of future chemistry revenue. We're now into the fifth quarter of strong bookings and revenue for that.
I think in the past, we talked about the first half of '26, our factories are full through then. I think we're not going to guide bookings going forward in equipment, but I would say the difference between 90 days ago is we continue to see strong bookings in chemistry equipment.
I think that continues, and that's really just something that over time will lead to that high gross margin chemistry revenue that will be on our production equipment.
Jim Ricchiuti
Thanks. A follow-up, you highlighted the improving demand in PCB drilling equipment.
How would you characterize the recovery that you're seeing in this part of the business versus previous cycles? I know it's been a while since we've seen a decent upturn in this business.
John Lee
I know you've covered ESI for a long time, Jim. I would say, there was a supercycle, maybe 4 or 5 years ago.
This is more like a normal cycle. It's probably 2 years now where it's kind of been more normalized.
We're happy to see that. We're happy to see that our share continues to be very strong, and that some new devices that we talked about, foldable phones, are driving more flex demand.
I think I would characterize this as not a supercycle, if you will, for flex, but more of a normalized cycle that we would have expected on a more consistent basis throughout the years.
Jim Ricchiuti
Thank you.
John Lee
Thanks, Jim.
Operator
Thank you, and one moment for our next question. Our next question will come from the line of Melissa Weathers with Deutsche Bank.
Your line is open. Please go ahead.
Melissa Weathers
Hi there. Thank you for the question.
John, I was hoping to ask you to pull out your crystal ball and get your opinion on WFE growth this year. We've heard some pretty strong outlooks from some of your customers and peers on WFE.
Any sense of magnitude or how are you guys thinking about the magnitude of growth the equipment spending could have this year, and then how should we think about that flowing through to your semiconductor system sales?
John Lee
Yes, I'll pull out my crystal ball, Melissa, and it's cloudy, but I guess it's positive. A couple of our etch customers are talking about 20% year-over-year WFE growth.
A couple of our litho metrology customers are talking more in the mid-teens, if you will. If you put it all together, WFE will be a large grower, and I think more importantly, everybody's kind of assuming it's more than just a 1-year thing, it's going to be a cycle that maybe lasts longer than that.
MKS has always outperformed during the upturn, that's just math. Everything's designed in already in an upturn.
People are just ordering things that are already designed in. We have to ship before our customers can ship.
At the same time, during a ramp, our customers are going to try to build inventory. All that leads to outperformance.
Even in 2025, when there wasn't really a ramp, I believe we will have shown that we outperformed WFE even in a relatively stable 2025. I would say in my commentary, a couple months ago, the ramp has started, we have started.
Supply chain teams are working hard with our suppliers. We're in constant communication with our customers, and everybody in the industry is getting ready for this ramp.
MKS, as is supporting 85% of WFE, we're going to see all of that, and we're really looking forward to meeting that demand. I think we also talked about the Malaysia plant, which will come online mid-year, and that will give us just extra flexibility in the future.
Our factories today are ready to meet the demand that we see in the next year or two.
Melissa Weathers
Perfect. Thank you.
Then maybe following up on something you've already touched on on the call, but the ability for the AI side of things to sort of offset any slowness that we could see in consumer electronics, and you talked about the board complexity and layer counts going up for AI boards. Is there any other way to quantify what is your revenue opportunity with a 2026 or 2027 board versus what you've seen in the past, just any other way to frame how we should think about that content opportunity and sort of how much that could offset any weakness on the consumer electronics side?
John Lee
Maybe the way to think about it is, let's take smartphones. The number of layers in the PCBs for smartphones could be that 10 to 12 layers give or take, and it's increasing as well.
The HDI type of boards for AI are in that 15 to 20 already. In addition, AI also needs multilayer boards, which are in the 30 to 40 layers.
Then, of course, the substrates, the package substrate layers. I would say that PCs and smartphones, the number of layers is consistent, it goes up a couple layers every cycle, but AI, we're talking about doubling the number of layers.
We've talked about in the past that our chemistry revenue from AI in 2024 was about 5% of chemistry revenue in electronics and packaging. Now in 2025, it's 10%.
I would say it's a sequential increase quarter on quarter on quarter in '25. We expect AI to continue taking a larger percentage of our chemistry revenue even with a slightly muted PC and smartphone market.
Melissa Weathers
That's super helpful. Thank you.
John Lee
Thank you, Melissa.
Operator
Thank you, and one moment for our next question. Our next question will come from the line of Michael Mani with Bank of America Securities.
Your line is open. Please go ahead.
Michael Mani
Good morning. Thanks so much for taking my questions.
To start, I just wanted to ask about your capacity position. With this Malaysia facility fully ramping over the course of next year, how much revenue do you think that could ultimately support for your business, and if there's any way to kind of quantify how much that footprint has expanded for you over the last couple years would be great.
Then as you look out, are there any other areas where you feel like you need to invest in your capacity position? I know there's a Thailand facility that you're ramping up, I believe that's for chemistry, but anywhere else where you anticipate any supply constraints?
Thank you.
John Lee
Yeah. Thanks, Mike, for the question.
I think with Malaysia, it was built as a business continuity plan. It wasn't built to anticipate, needed more capacity for this particular ramp.
We already have plenty of factory capacity for that. I think Malaysia is kind of think about it as future capacity needs for WFE.
We haven't sized it. I would say this: we always build our factories in phases.
We have the shell, and then we'll put in a certain amount of lines and product lines, beginning middle of this year, and then we'll plan on what makes sense to grow there. It will give us a lot more capacity than than we have currently.
I would say we've added a little bit of capex here and there, kind of nip and tuck with our factories in anticipation of this particular cycle, but we had talked about being ready for $125 billion WFE 3 years ago, and we did that. Remember that $125 billion is run rate.
We always have 30% of surge capacity on addition to that. I think we're quite comfortable with our capability.
I think always in in a ramp, the constraints are, supply chain. Our suppliers are better, they're bigger, they're ready, but, the golden screw effect will happen.
That's really where our execution has always been among the best, is finding those those issues and then dealing with them and delivering to our customers on time. We've always done that through every cycle, I'm very confident we'll have the capacity, we have the team, and the supply base to help us deliver to our customers this ramp as well.
Michael Mani
Very helpful. Thank you.
Moving on to electronics and packaging, so as you look out over this next year, is it fair to say that most of the growth this year if it is sustainable in this kind of double-digit growth area would largely come from more chemistry revenue now that you've seen significant equipment orders over the last couple months that are going to be ramping in terms of utilization? Then more broadly, and this kind of relates to the previous question, I think in the past you've said that every $100 million in installed equipment translates to $20 to $40 million in chemistry sales per year for wheel utilization.
Just wanted to ask, what are the sensitivities around that? Is the revenue function much higher if it's a substrate versus MLB, and as your customers are talking about pushing the number of layers to over 100, what does that do to that attach rate for revenue?
Thank you.
John Lee
Thanks, Michael. I think in general, our model is still the same, $20 to $40 million is per $100 million of equipment sales.
Doesn't really change too much between particular types of boards, and it's really a function of utilization. If that tool is running 100%, then you're getting into that $20 to $40 million range.
Then, I think in general we're just very happy with the continued shipments of our equipment. As I said in the earlier question, continues to get better.
It continues to be consistently strong, even from a quarter ago. If that's the case, then we will have had potentially 2 good years of record-level chemistry equipment shipments.
Ram Mayampurath
Now, I also think we've talked about how long does it take for a piece of equipment to turn into chemistry revenue. We've said 18 to 24 months, that's still the case.
A lot of the chemistry revenue that you saw grow in 2025 was with equipment we shipped in 2021, 2022. That's why I think the equipment we're shipping now will be great capacity for future chemistry going forward into '26, 20 end of '26, '27, and going forward.
Just want to make sure that was clear, that chemistry revenue now is not constrained by the equipment we're shipping. That chemistry revenue is growing because of the capacity we've already shipped in terms of equipment a few years ago.
Michael Mani
Thanks, John.
John Lee
Thanks, Michael.
Operator
Thank you, and one moment for our next question. Our next question comes from the line of Shane Brett with Morgan Stanley.
Your line is open. Please go ahead.
Shane Brett
Thank you for letting me ask a question. I want to follow up on Mani's question.
Just based on the knowledge you currently have, should we be anticipating chemistry revenue to accelerate or decelerate in 2026? I'm asking this because I want to better figure out just how much of this chemistry revenue is associated with just higher growth AI or should be kind of benefiting from a higher install base, but how much could be impacted by just weaker consumer electronics sales?
Thank you.
John Lee
Shane. I think, well, there is a seasonality to the chemistry revenue, as Ram pointed out.
Q1 is for the consumer product cycle type of products is lowest because of Lunar New Year, and then the consumer products chemistry will continue to grow throughout the year, that's the consumer product cycle. To your point, if there's a low single-digit decrease, then we'll see that in that chemistry revenue for that market.
At the same time, we are expecting that to continue to grow. All our customers that are in that AI supply chain are running capacity, they continue to add tools, and add and bring those tools up.
I think as I said, that's why I expect that even with a slight decrease in PCs and smartphones, the AI part of the chemistry will more than make up for that.
Shane Brett
Got it. Thank you.
For my follow-up, on the E&P tooling side, late last year you sort of mentioned that you're booked through the first half of 2026. Just how should I think about your current capacity for E&P tools relative to the existing demand for these tools?
Thank you.
John Lee
I think we've added some capacity. We didn't need to build a new factory if that's your question.
We've been able to meet the timing demands of our customers even at these elevated levels. As I said, earlier in the commentary, based on changes from 90 days ago, we continue to see these strong bookings.
I think it's going to be another strong year for equipment, and our capacity to meet the timelines needed by our customers right now is sufficient. We're not constraining our customers.
Shane Brett
Thank you.
John Lee
Thank you.
Operator
Thank you, and one moment for our next question. Our next question comes from the line of David Lu with Mizuho.
Your line is open. Please go ahead.
David Lu
Hi. Thank you for letting me ask the question.
On for Vijay at Mizuho. Maybe a first one, just back on WFE, I think your customers and peers have mentioned second-half weighted strength and acceleration.
Do you think we can see that semi revenue hit probably a five five handle starting in September, December?
John Lee
Sorry, David. A five handle on...
David Lu
Semi's revenue.
John Lee
Semi's revenue, I see. We're guiding 450 or something like that.
I would say this, WFE grows in that same range between 15% to 20% as so many of our customers are saying. We're going to have to ship ahead of that.
We're going to have to ship to build that revenue for their inventory. I think in the past, we have hit that five handle at the last ramp.
That wasn't constraints from our factory, that was constraints from supply chain, right? I think we're better at managing supply chain, I think supply chain is better.
A five handle would not be surprising, I just can't predict when it would be. In order to meet a 20% WFE increase, we have to get to a five handle probably as MKS, otherwise the industry won't get to that 20%.
David Lu
Got it. Then, a longer term question, I think part of the industry is beginning to look at moving to panel for advanced packaging.
Just wondering what kind of conversations you guys are starting to have there in the advanced packaging side, and if there's any sort of outlook or timeline that benefits MKSI?
John Lee
I think you were referring to redistribution layers going from wafer shapes to panel rectangular shapes, and I think many customers are working on that. Of course, when they go to panel, that's MKS.
We are participating in the wafer type of packaging, but our strength has always been in panels. That is a tailwind for MKS, but as I've mentioned in the past, that's kind of one or two layers of redistribution layers, and that is still relatively small in terms of market growth for us because the HDI and MLB are growing at 10 layers a year or more each.
While it's a tailwind, I think we don't want to miss the bigger picture, which is that the number of layers of MLB and HDI and package substrates are growing much faster.
David Lu
Thank you.
Operator
Thank you, and as a reminder, if you would like to ask a question, please press star one one on your telephone. Our next question will come from the line of Peter Peng with J.P.
Morgan. Your line is open.
Please go ahead.
Peter Peng
Hey, guys. Thanks for taking my question.
Some of your semi customers are already talking about inventory build. Have you seen that in the second half of 2025, or are you starting to see that now in terms of inventory build?
John Lee
Yeah. You can look at their inventory numbers and you'll see if it's building.
I would say this, Peter, a lot of the conversations on getting ready happened in that Q4 timeframe, and they have continued to accelerate in the Q1 timeframe. We're ramping our factories and our supply chain, and I think it will take a little while to show up as inventory build in our customers, because right now as a supply chain, we're all just getting ready to just meet the higher demand.
You'll probably see that build up in their inventory numbers over the next couple quarters, but we are still shipping to demand at this point just because we're just in the early stages of that ramp.
Peter Peng
Got it. Then into the electronics and packaging, there's a lot of, I guess, constraints and greenfield capacities, even from your end customers.
As you kind of engage, are you seeing any constraints from your customers where they just don't have enough space to move equipment yet, and so maybe you can talk about that dynamic?
John Lee
I have not heard that, Peter. I think our customers are well-run customers.
They have large factories located globally. At the last ramp, we all added capacity, got more efficient.
I don't see that as a constraint in terms of not enough space to build the tools, if that was your question.
Peter Peng
Yeah. Okay.
Thank you.
John Lee
Thanks.
Operator
Thank you, and one moment for our next question. Our next question comes from the line of Joe Quatrochi with Wells Fargo.
Your line is open. Please go ahead.
Joe Quatrochi
Thanks for taking the questions. Maybe just kind of on that line of thinking on the semi business, you're guiding for kind of 3-ish percent sequential growth, and I think some of your main customers are guiding for high single-digit, low double-digit sequential growth for the first quarter, just kind of curious if you could kind of give us the puts and takes there?
John Lee
Joe. I think we're guiding based on our best view today.
I think you've been in this industry a long time, when that ramp occurs, it just accelerates fast. This is our best view today, but during a ramp, as things can accelerate rapidly.
We're going to stick to this guidance, but certainly we give a range. Even last quarter, right, we gave a range, and we went higher than that upper end of that range, and that's kind of a characteristic of ramps.
This is what we see today. I would say this: if we could ship more, our customers would probably take it.
We're trying to ramp as fast as we can.
Joe Quatrochi
That's helpful. Then maybe just as we think about the ramp through the course of the year and think about just the puts and takes on gross margin, should we still think about 50% as kind of incremental gross margin leverage, just thinking about the tariff dynamic as well?
Ram Mayampurath
Yeah. Hi, Joe.
This is Ram. I'll take that.
The quick answer is yes. We are very pleased with the gross margin for 2025.
If it weren't for tariffs, we would have been to your point, or 47%. If you remember, last three quarters we were focused on mitigating the cost of the tariffs, and by Q4 we offset the cost dollar for dollar.
Going forward, we'll be focused more on mitigating the impact on the gross margin itself. Yes, the volume and the right mix will certainly get us back to the 47%.
Joe Quatrochi
Thank you.
Operator
Thank you. Again, if you would like to ask a question, please press star one one on your telephone.
Our next question will come from the line of James Schneider with Goldman Sachs. Your line is open.
Please go ahead.
James Schneider
Good morning. Thanks for taking my question.
Just as a clarification initially, you talked about your semi customers citing a 15% to 20% outlook and your ability to kind of do towards the high end of that presumably given the mix of your customers and the mix of your business. You had also just referenced potential constraints in terms of ramping your production.
Can you maybe just give us clarity on whether you see yourselves as constrained in your ability to ship in the next two quarters, do you think you'll be kind able to catch up to your customers' full demand, unconstrained demand run rates by the middle of the year at least?
John Lee
I would say this, Jim. During the beginning of a ramp, we're never the constraint because I think we have a supply chain with inventory as well.
Even during the peak ramp and even after many quarters of a ramp, we have never constrained our major customers. I think it's an industry that's always met demand as a entire semiconductor industry.
Companies that don't meet demand and constrain their customers, they're not around anymore, right? I think we have plenty of capacity.
The challenge is getting the supply chain to ramp up, but even then, our biggest customers have always been a priority, and we've never disappointed them.
James Schneider
Very clear. Thank you.
Then just in terms of how we think about the forward model, you've clearly stated that you expect to grow opex slower than revenue, but give us a sense about the level of leverage you expect there, please. 2 to 1, or etcetera?
Ram Mayampurath
Yeah. Hi, Jim.
We watch our opex very carefully, but we will be investing this year to support the growth. In terms of leverage, that will be a focus to drive our leverage further.
If you look at '24 to '25, our opex dollars grew, but our opex as a percentage of sales was lower. We finished around 26% for '25, and '26 will be lower than that.
James Schneider
Thank you.
Operator
Thank you, and I would now like to hand the conference back over to Paretosh Misra for closing remarks.
Paretosh Misra
Thank you all for joining us today and for your interest in MKS. Operator, you may close the call, please.
Operator
This concludes today's conference call. Thank you for participating, and you may now disconnect.