GAAP gross profit for the fourth quarter 2015 was $53.9 million, or 25.1 percent of revenue, including $3.1 million inventory valuation adjustments related to the Pericom acquisition. Non-GAAP gross profit, excluding the $3.1 million inventory adjustment, was $56.9 million, or 26.5 percent of revenue. GAAP gross profit in the third quarter 2015 was $61.6 million, or 29.5 percent of revenue, and in the fourth quarter 2014 was $70.7 million, or 31.6 percent of revenue. The sequential decline in gross profit margin was due to lower capacity utilization, product mix and pricing.

Operating expenses for the fourth quarter 2015 were $52.8 million, or 24.6 percent of revenue, compared to $51.7 million, or 24.7 percent of revenue, in the third quarter 2015 and $48.6 million, or 21.7 percent of revenue, in the fourth quarter 2014.

Fourth quarter 2015 GAAP net income was $0.7 million, including $4.1 million of Pericom acquisition-related expense, or $0.01 per diluted share, compared to third quarter 2015 of $2.8 million, or $0.06 per diluted share, and fourth quarter 2014 of $16.7 million, or $0.34 per diluted share.

Fourth quarter 2015 non-GAAP net income was $6.7 million, or $0.14 per diluted share, which excluded, net of tax, $3.2 million of purchase price accounting costs, $2.4 million of non-cash, acquisition-related intangible asset amortization costs and $0.4 million of severance costs. This compares to non-GAAP net income of $6.3 million, or $0.13 per diluted share, in the third quarter 2015 and $18.3 million, or $0.38 per diluted share, in the fourth quarter 2014.

The following is a summary reconciliation of GAAP net income to non-GAAP net income and per share data, net of tax (in thousands, except per share data):