GAAP operating expenses for first quarter 2017 were $64.6 million, or 27.3 percent of revenue, and $57.3 million, or 24.2 percent of revenue, on a non-GAAP basis, which excludes $4.8 million of amortization of acquisition-related intangible asset expenses, $2.3 million of KFAB restructuring charges and $0.2 million of retention costs. GAAP operating expenses in the fourth quarter 2016 were $61.9 million, or 26.7 percent of revenue, and $56.5 million or 24.3 percent of revenue, on a non-GAAP basis.

First quarter 2017 GAAP net income was $1.2 million, or $0.02 per diluted share, compared to $1.3 million, or $0.03 per diluted share, in fourth quarter 2016, and a net loss of $1.7 million, or ($0.04) per share, in first quarter 2016.

First quarter 2017 non-GAAP adjusted net income was $7.0 million, or $0.14 per diluted share, which excluded, net of tax, $3.9 million of non-cash acquisition-related intangible asset amortization costs and $1.8 million of restructuring costs related to KFAB closure accruals. This compares to non-GAAP adjusted net income of $7.7 million, or $0.15 per diluted share, in fourth quarter 2016 and $5.9 million, or $0.12 per diluted share, in first quarter 2016.

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