Doug Bettinger
Executive Vice President, Chief Financial Officer at Lam Research
Great. Thank you, Tim. Good afternoon, everyone and thank you for joining our call today during what I know is a busy earnings season.
We had a record financial year in calendar 2022. Our revenue came in at $19 billion and we delivered an all-time high for earnings per share of $37.31, which was a 15% growth in earnings per share over calendar year '21. Overall, I am pleased with the operational performance we achieved this past year, delivered while navigating a challenging business environment with global supply chain constraints, significant inflationary headwinds and fluid regulatory restrictions.
Lam also achieved record levels of performance in the December '22 quarter across multiple metrics, including revenue, operating income dollars and earnings per share. Revenue for the December quarter was $5.28 billion, an increase of just over 4% from the prior quarter. We delivered higher levels of system sales in deposition and etch offset somewhat by a decrease in CSBG revenue.
Deferred revenue at the end of the quarter was $2 billion, a decline of $770 million from the September quarter. Supply chain constraints have improved and we were able to fill shipments of many critical parts that's required for revenue recognition. Our expectations are that the deferred revenue balance will continue to decrease in the March quarter as we fully complete shipments related to outstanding backordered systems. The deferred revenue balance decrease I just spoke about was partially offset by some increases in deferred, due to customer cash and advanced deposits, which I also noted last quarter.
As we sit here today, I expect to have some level of these type of deposits in the deferred balance throughout calendar 2023, keeping deferred revenue at somewhat higher levels than we have historically seen. I anticipate that the deferred revenue from backorders will be at a normalized level as we exit the March quarter.
Let's turn to the revenue segment details for the December quarter. Memory represented 50% of systems revenue, which is slightly down from the prior quarter level of 52%. Included in memory, the NAND segment represented 39% of our systems revenue, flat with the September quarter. The spending was primarily focused on 192 layer and above class devices.
The DRAM segment concentration decreased sequentially from the prior quarter, coming in at 11% of systems revenue compared to 13% in the September quarter. The DRAM investments were mainly targeted towards 1Z and 1-alpha nodes. I expect that we will see both NAND and DRAM revenue decline meaningfully in the March quarter. For calendar 2023, I expect NAND spending to decline more than DRAM.
We continue to see strength in the foundry segment with the December quarter concentration comprising 31% of our systems revenues. While this percentage is a little bit lower than September quarter level of 34%, the dollar amount was flat with a mix of investments in both leading and mature node devices.
The logic and other segment revenue came in at a high watermark for the company, contributed 19% of systems revenue in the December quarter compared with 14% in the prior quarter. Investments were focused on microprocessor, image sensor and advanced packaging technologies. Lam had strong momentum in logic and other throughout calendar 2022. I expect, we will continue -- excuse me, to perform well in this segment. I'd mention that this was a record revenue level for us in microprocessor related revenue. We have been talking about momentum here for a while and it's clearly showing up.
With respect to the regional composition of our total revenue, the China region was 24% of the total, down from the prior quarter level of 30%. This reduction was due to the U.S. government sales restrictions for certain domestic customers, which were put in place in early October of 2022. Rounding up the top region of revenue locations, Korea comprised 20% of total revenue, up from 17% in the prior quarter and Taiwan decreased to a concentration of 19% compared to 22% in the September quarter.
The customer support business group results in the quarter were approximately $1.7 billion, which was down 9% from the September quarter, though it was 16% higher than the December quarter of calendar 2021. As I have noted in the past, CSBG revenues will fluctuate on a quarterly basis. And in the December quarter, we experienced declines in the CSBG product lines with reductions in utilizations and system spending.
Going into calendar 2023, we have the impact of China regulatory restrictions in addition to memory spending at well below historic levels and elevated customer device inventory. These factors are resulting in customers having underutilized factories and taking actions to manage their supply levels in 2023, negatively impacting our spares and services business. While we continue to believe the mature node segment will perform better than overall WFE spending, we are in an unprecedented business environment and expect the CSBG business could be down somewhat in calendar year 2023.
Let me now pivot to our gross margin performance. The September quarter came in at 45.1% over the midpoint of the guided range, but down from September quarter's gross margin of 60% -- about 46%. The decrease from the September quarter was tied to customer and product mix. With the decline in business volumes in March 2023 quarter, we expect lower factory and field utilizations to unfavorably impact our gross margin on a sequential basis.
Operating expenses were $686 million in the December quarter, up 6% from the prior quarter amount of $647 million. The higher spending was mainly in R&D projects, which comprised nearly 67% of our total spending. Supporting our customers' roadmap continues to be a top priority for us, while we focus on managing other areas of discretionary spending within the company.
December quarter operating margin was 32.1% over the midpoint of guidance due to the higher level of revenue and gross margin. Our non-GAAP tax rate was 11.9%, in line with expectations. Looking into calendar 2023, we believe the tax rate will be in the low to mid-teens with some fluctuations quarter-by-quarter. This rate estimate does not include any impacts from potential U.S. or global tax policy changes.
Other income and expense came in for the quarter at $38 million of expense, approximately $9 million higher from the prior quarter, mainly due to negative foreign exchange fluctuations which was somewhat offset by higher interest income because of increasing returns on our cash and investments.
OI&E will continue to be subject to market-related fluctuations that will cause some level of volatility quarter-by-quarter. On the capital return side in the December quarter, we allocated approximately $483 million to open market share repurchases. Additionally, we paid $236 million in dividends in the quarter.
For the 2022 calendar year, we returned 119% of our free cash flow, totaling $3.5 billion which was somewhat higher than our long-term capital return plans of 75% to 100%. December quarter diluted earnings per share was $10.71, which was at the high-end of our guidance range, diluted share count was 136 million shares, which was lower than the September quarter and in line with our December quarter expectations. During 2022, we lowered share count by nearly 6 million shares through our share buyback program.
Now moving to the balance sheet, our cash and short-term investments, including restricted cash, were up to $4.8 billion versus the prior quarter level of $4.6 billion. Operating cash flow of $1.1 billion in December quarter was offset by cash allocated to share repurchases, dividend payments and capital expenditures.
Inventory turns were 2.4 times. Days sales outstanding were 70 days, a decrease from 82 days in the September quarter due to strong collections and improved linearity within the quarter. I would point out that we expect 2023 to be a strong cash generating year as working capital comes down with lower business levels. Our non-cash expenses for the December quarter included approximately $73 million for equity compensation, $73 million in depreciation and $12 million in amortization. Capital expenditures for the December quarter were $163 million, a slight increase over the September quarter spending of approximately $140 million. The expenditures were in R&D and manufacturing, including our Korea Technology Center and our Malaysia factory.
We ended the quarter with approximately 19,200 regular fulltime employees, which was an increase of approximately 500 people from the prior quarter. Our growth was in the factory and field to support the manufacturing as well as installation of tools at our customers' fabs. Also included in this headcount growth, were 150 employees from the SEMSYSCO acquisition that was completed in the December quarter. As you heard from Tim and saw in our earnings release, we will be reducing our regular fulltime headcount by approximately 1,300 employees. We expect these reductions to be largely reflected in our June quarter ending headcount. In addition to the fulltime reductions, we expect to be lowering our temporary workforce by approximately 700 people in the March quarter. We've already adjusted our temporary workforce down by 700 people in the December quarter.
Let me now turn to our non-GAAP guidance for the March 2023 quarter. We're expecting revenue of $3.8 billion plus or minus $300 million. I'll also just mention that we currently think revenue will be somewhat first half weighted this year as we consume the reduction in deferred revenue in the March quarter.
Gross margin of 44% plus or minus 1 percentage point, the decrease in this is the result of lower business volumes. Operating margin of 27.5%, plus or minus 1 percentage point; and finally, earnings per share of $6.50 plus or minus $0.75 based on a share count of approximately 135 million shares. We will be taking a charge of approximately $80 million in the March quarter from headcount reduction. Including this impact, and the other near-term actions that Tim spoke about, we are anticipating a total of $150 million to $250 million in charges to be incurred over the next 12 months. In addition to headcount, we anticipate potential charges from facilities restructuring, business realignment and transformation and product rationalization.
On top of the cost savings activities, we are driving a greater focus from our senior leadership team through inclusion of additional profitability metrics in our annual incentive compensation structure. Currently, we're at low volumes given the business environment. These initiatives will structurally improve our profitability. As Tim already laid out, we expect gross margin to be higher by roughly 1 percentage point and to expand operating margins by a little more than that as we exit the calendar year and complete these activities.
Over many years in cycles, Lam has established a proven track record of successfully managing this business. With the actions we plan to execute throughout the year, we expect to strengthen our operations and technology leadership and further enhance our profitability profile with the company's returning growth. When business improves, and we know it will, Lam will be a stronger, better positioned, more efficient company.
Operator that concludes our prepared remarks, we would now like to open up the call for questions.