Doug Bettinger
Executive Vice President and Chief Financial Officer at Lam Research
Great. Thank you, Tim. Good afternoon, everyone, and thank you for joining us on our call today. Lam's delivered another quarter of strong results with revenue, operating income dollars and earnings per share coming in at record levels in the September quarter. All financial metrics came in at or above the midpoint of our guidance, demonstrating our continued focus on operational execution. We've achieved this performance while also navigating significant supply-chain challenges. We're pleased with Lam's ability to scale the company in this demanding environment. September quarter revenue was $4.3 billion, an increase of 4% from the June quarter and more than 35% growth from a year ago.
Looking at the breakout of the Systems revenue, the Memory segment represented 64% of Systems revenue in the September quarter, which was up from the prior quarter level at 59%. Memory growth was driven by investments in DRAM, primarily in the 1z and 1-alpha nodes. DRAM Systems revenue nearly doubled in dollar terms and grew from 10% in the June quarter to 19% in the September quarter. NAND segment concentration came in at 45% of our Systems revenue versus 49% in the June quarter and was flattish in dollar terms.
Our NAND customers are investing in both capacity additions and conversions with equipment investments focused towards 128-layer through 192-layer devices. The Foundry segment spending represented 25% of our Systems revenue compared with 35% in the June quarter. We're seeing investments in equipment from both leading-edge and mature device nodes from multiple sources of end-use demand such as AI, IoT, cloud and 5G. Logic and analog device companies are driving capacity additions at the foundries.
There is notable growth in the Logic and Other segment, which hit a record level of Systems revenue for Lam in the September quarter. Logic and Other contributed 11% of Systems revenue in the September quarter which was up from 6% in the June quarter, and it was driven by leading edge and mature nodes ramping from microprocessors, image sensors, core management and 5G demand. Let me turn now to the regional composition of our total revenue. The China region came in at 37% of total revenues which was flat with the prior quarter percentage level.
The revenue from China domestic customers and multinational customers with fabs located in China was again fairly balanced in the September quarter. Korea and Taiwan regional spending represented 21% and 15% of revenues respectively in the September quarter. I do expect that the December quarter revenue will have a lower China concentration. The customer support business group revenue was nearly $1.4 billion, 34% higher than the September quarter in calendar 2020 and flat with the prior-quarter level.
As Tim noted, the Reliant product line that serves the specialty market delivered record results and we also had solid results in the spares, service and upgrades side with the focus on maximizing the productivity and value of the installed base tools while supporting the high fab utilization levels in the industry. I continue to have confidence that CSBG will grow revenues consistently on an annual basis. Let me now hit the margins performance. Our September quarter gross margin was 46% right at the midpoint of our guided range. I just remind you that our gross margin can fluctuate quarter-to-quarter due to overall business levels along with customer and product mix.
The supply chain constraints discussed earlier have resulted in elevated costs broadly with freight and logistics costs continuing to be one of the biggest headwinds. Additionally, we currently have margin dilution from our new factory in Malaysia which is not yet operating at full capacity. We've included these costs in our December quarter guidance as we expect they will remain in the near future. Operating expenses for September were $586 million, a slight increase from the prior quarter.
We've continued to manage our expenses as we scale the company, with a strong focus on operational efficiencies while prioritizing R&D spending to deliver differentiated product portfolio that supports our customers technology roadmaps. September operating margin exceeded the midpoint of our guidance range at 32.4% or approximately $1.4 billion. Our non-GAAP tax rate for the quarter was 12.2%, generally in line with our expectations. And as we've noted in previous quarter calls, our tax rate may fluctuate from quarter to quarter, and you should expect the ongoing tax rate to be in the low teens level for the 2021 calendar year.
We continue to monitor potential tax changes under consideration in the United States, but we've not reflected the impact of any potential changes in our financial models at this point. Other income and expense came in for the quarter at $36 million in expense. This amount is higher than prior quarter due to an unrealized gain we had in June for one of our private equity investments partially offset by lower interest expense in the September quarter as a result of the payoffs of our 2021 notes last quarter. And just to note, OI&E is subject to market-related volatility that could cause a difference from our typical run rate.
We were active in our buybacks during the September quarter allocating over $1.2 billion towards share repurchases. We deployed this cash and a combination of open market repurchases as well as an accelerated share repurchase program. This ASR will continue to execute in the December quarter. In addition, we paid $185 million in dividends in the quarter. I'd also like to highlight that in August we announced a 15% increase in our quarterly dividend, growing it from $1.30 to $1.50 per share which was paid in October. We're tracking very well to our capital return plans with returns of over 100% of our free cash flow year-to-date in calendar year 2021.
Diluted earnings per share for the September quarter was $8.36, above the midpoint of the guidance range. The diluted share count balance was down slightly from the June quarter level coming in at 143 million shares, generally in line with our expectations. Let me now shift to the balance sheet. Cash and short-term investments including restricted cash totaled $4.9 billion, which was down from the prior quarter. The decrease in cash is attributed to the capital return activities that I described earlier. Additionally, the timing of shipments and resulting impact on accounts receivable as well as an increase in our inventory balance consumed cash in the quarter.
Days sales outstanding was up to 72 days from 66 days in the June quarter. Inventory turns were down slightly from the prior quarter level, coming in at 3.2 times, which was planned as we've increased inventory levels to meet the increasing investments from our customers as well as to help mitigate the challenges that we've seen in our supply chain. Non-cash expenses for the September quarter included approximately $58 million for equity compensation, $61 million for depreciation and $19 million for amortization. Capital expenditures for the September quarter were up versus the June level coming in at $136 million.
The increase in our expenditures is associated with capacity expansion in the network, in particular at our critical spare parts facility in Ohio, as well as spending for our Korea Technology Center that will be formally opening in 2022. We expect to see elevated levels of capital expenditures in the remainder of calendar year 2021 and into 2022 as we support the growth that we see in the business. We ended the September quarter with approximately 15,400 regular full-time employees, which is an increase of approximately 1,300 people, to meet the increased output levels and to support customers with their technology and production requirements.
Let's now take a look at our non-GAAP guidance for the December 2021 quarter. We're expecting revenue of $4.4 billion plus or minus $250 million. We continue to maintain a widened revenue range given the supply chain uncertainties that we mentioned. Gross margin of 46% plus or minus 1 percentage point, operating margins of 32% plus or minus 1 percentage point, and finally earnings per share of $8.45, plus or minus $0.50, based on a share count of approximately 142 million shares. And just an additional note, our guidance does not include an estimated gain related to one of our private equity investments that recently raised capital in a public offering. The gain as of today is in the $50 million range and is subject to market volatility.
The amount recognized in our financials as of the end of December 2021 quarter may fluctuate and I'll obviously give you an update at our next earnings release. So then in closing, we're experiencing ongoing output challenges in our global supply chain that are continuing to negatively impact both our revenue and gross margin. We're improving known items while new items continue to emerge that we need to further work through.
Lead times remain stretched, and we continue to have unmet demand. Despite these constraints, we're operating at record levels in terms of revenue and earnings while delivering the technology solutions our customers require. Industry demand remains strong as we look forward to growth in 2022. I remain very excited about the multitude of opportunities for the company, and I'd obviously like to thank the dedicated Lam Research employees for their tireless support in this environment.
Operator, that concludes my prepared remarks. Tim and I would now like to open up the call for questions.