Based on AWSC 2 μm HBT process, a power amplifier applied in 5G N77 frequency band (33～42 GHz) was designed. The gain, output power and power added efficiency of the power amplifier were significantly improved by using transformer matching. The problem of difficulty for matching the inter-stage of amplification circuits was solved. Simulation and test results showed that in the N77 operating band, the power amplifier had a gain of 36~38 dBm, an output power 1 dB compression point of 37 dBm, a power addition efficiency of 493 % at 1 dB compression point output power, a power addition efficiency of 165 % at 285 dBm output power, and an adjacent channel leakage ratio of -382 dBc.