The performance of high-efficiency millimeter-wave (mm-wave) power amplifiers (PAs) implemented in a 45-nm silicon-on-insulator (SOI) process is presented. Multistage class-AB designs are investigated for Q- and W-bands and a push-pull amplifier is investigated at Q-band. The Q-band, class-AB PA achieves a saturated output power of 15 dBm and power-added efficiency (PAE) of 27% from a 2-V supply. The W-band, class-AB PA achieves a saturated output power of 12.4 dBm and PAE of 14.2% from a 2-V supply. The performance demonstrates the high efficiency possible for mm-wave PAs in a SOI process.