The breakdown by application and market segment was as follows. Applications for the 4x technology node and below represented 91% of overall system shipments, and the memory segment accounted for 40% of all systems shipments, with NAND at 30% and DRAM at 10%. Foundry accounted for 53% of overall system shipments, while logic and other constituted the balance of 7%.
March quarter revenues came in at the high end of our guidance range at $659 million, up 13% over the prior quarter. Non-GAAP gross margin was at 40.9%, up sequentially from 40.1% and is consistent with our expectations of customer concentration and mix, offsetting improvements in factory utilization from the increased business levels.
As planned, non-GAAP operating expenses for the quarter increased to approximately $197 million versus $180 million in the December quarter. More than 70% of this incremental spend was focused on next-generation R&D and the customer-facing activity that surround and support it. The balance of the operating expense change was attributable to higher variable compensation expenses associated with higher profit levels, as well as expenses related to market appreciation of deferred compensation plan assets.
Lam intends to mitigate overall exposure relative to market fluctuations impacting these plans, and this quarter is no exception. The increased operating expenses related to these plans were substantively offset by increased income in other income and expense.As we indicated on our last call, we remain committed to keeping Lam standalone operating expenses at or below $200 million per quarter. Non-GAAP operating income was $73 million versus $54 million in the December quarter and resulted in a non-GAAP operating margin of 11.1%, slightly better than the midpoint of our guidance range. Our non-GAAP tax rate for the March quarter was 20.4% compared to 21.8% in the prior quarter. On a Lam standalone basis, we estimate the June quarter tax rate to be in the mid-teen, bringing our fiscal year non-GAAP tax rate to around 20%. This rate would be favorably impacted by approximately 2% should Congress extend the federal R&D tax credit prior to the end of our fiscal year. Read the rest of this transcript for free on seekingalpha.com