ASP, average selling price, at $1.81 versus $1.83 last quarter was relatively constant. A slight improvement in gross margin percentage was due to absorbing certain fixed costs over a larger sales base.
Operating expenses increased $7.3 million, of which roughly $5 million was due to operating expenses of Dust Networks, which we acquired at the end of last quarter, and also due to additional labor costs in the R&D and SG&A areas in Linear's base business. We had a shutdown in these operating expense areas last quarter but not this quarter, thereby increasing the March quarter labor expenses.
Operating income at 44.8% of sales, down from 45.2% last quarter, was in our forecasted range, having been impacted by the increased costs just discussed. Below the line, interest income and expense were unchanged. Finally, income taxes decreased due to a one-time discrete tax benefit. Our quarterly effective tax rate was 23.75% compared with 26.25% last quarter. The resulting net income of $98,499,000, an improvement of $10.6 million over last quarter, is due mostly to the increase in sales.
Our return on sales was 32% versus 30% last quarter. Headcount decreased marginally through the reductions in our overseas manufacturing plants.In summary, the effects of the items I just listed on the published quarterly results was that revenue was $312.4 million for the quarter, the third quarter of fiscal year 2012, compared to the previous quarter's revenue of $294.3 million and compared to $353.2 million reported in the third quarter of fiscal 2011. GAAP diluted earnings per share of $0.42 increased $0.04 from the previous quarter's earnings per share and decreased $0.19 from the $0.61 per share reported in the third quarter of fiscal 2011, which had benefited from higher sales and a low quarterly effective tax rate of 17%. GAAP net income was $98.5 million compared with $87.9 million last quarter and $141.6 million reported in the third quarter of last year. Earnings per share would be $0.49 on a pro forma basis, which excludes the impact of stock option accounting and the amortization of debt discount, which is the theoretical difference between the company's convertible debt, actual interest and the interest it would potentially have had to pay if it had used straight bank debt.