Gross profit, expressed as a percentage of revenue, was 49.7 percent this quarter. This is higher than both the 47.7 percent of revenue reported in the same quarter a year ago, and 48.2 percent last quarter. Compared to the year ago quarter, gross profit percentage increased primarily due to lower manufacturing costs and benefits associated with a weaker Japanese yen versus the U.S. dollar, partially offset by lower sales volume. The increase in gross profit percentage versus the previous quarter was primarily due to lower fixed manufacturing and logistics costs, and the favorable impact of the weaker Japanese yen. Year to date, gross profit represented 48.3 percent of revenue, which is above the company's full fiscal year guidance range of 46 to 48 percent of revenue, which remains unchanged.
Operating expenses, which include research, development and technical, selling and marketing, and general and administrative expenses, were $32.4 million in the third fiscal quarter, or $1.2 million less than the $33.6 million reported in the same quarter a year ago, primarily due to lower depreciation expense, clean room materials expense and staffing related expenses. Operating expenses were $2.0 million lower than the $34.4 million reported in the previous quarter, primarily due to lower staffing related costs. Year to date, total operating expenses were $100.2 million. The company's full year guidance for operating expenses remains unchanged at $132 million to $136 million.
Net income for the quarter was $15.5 million, or 17.0 percent higher than the $13.2 million reported in the same quarter last year, and 64.5 percent higher than the $9.4 million in the previous quarter. Compared to the same quarter last year, net income was higher primarily due to a higher gross profit margin, a favorable impact of the weaker Japanese yen reflected in other income, lower operating expenses, and a lower effective tax rate, partially offset by lower revenue. The effective tax rate in the third fiscal quarter decreased primarily due to the company's recent election to permanently reinvest the earnings of its Japan subsidiaries. Compared to the prior quarter, net income was up $6.1 million mainly due to the company's higher level of sales, higher gross profit margin, lower operating expenses and a lower effective tax rate. Year to date, net income of $34.6 million was up 18.6 percent compared to the prior year.
Diluted earnings per share were $0.65 this quarter, which includes a $0.05 benefit associated with the company's permanent reinvestment election in Japan, up from $0.55 reported in the third quarter of fiscal 2012 and up from $0.40 reported in the previous quarter. Year to date, diluted earnings per share of $1.46 were up 17.7 percent compared to last year.
Cabot Microelectronics Corporation's quarterly earnings conference call will be held today at 9:00 a.m. Central Time. The conference call will be available via live webcast and replay from the company's website, www.cabotcmp.com, or by phone at (866) 318-8612. Callers outside the U.S. can dial (617) 399-5131. The conference code for the call is 62171186. A transcript of the formal comments made during the conference call will also be available in the Investor Relations section of the company's website.