A W-band power amplifier in 65-nm CMOS technology is presented in this paper. This PA is a 3-stage common source design using thin film microstrip lines to realize the matching network. Choosing high-pass topology for the inter-stage matching network and low-pass matching for the input and output to compensate device frequency response, we achieve a wide band and high output power PA. From the measurement results, under 1.2 V supply voltage, the small signal gain of this PA is 12 dB with 27 GHz 3-dB bandwidth (79-106 GHz). The saturated output power is 14.8 dBm, and P1dB is 12.5 dBm. This W-band PA demonstrated widest bandwidth among the reported CMOS PA in this frequency regime, with state-of-the-art output power performance, and a miniature size.