Based on the 90 nm InP HEMT process, a 220 GHz power amplifier Terahertz Integrated circuit design (TMIC) is designed. The amplifier adopts the on-chip Wilkinson power divider structure to realize the power synthesis of two-way five stage common-source amplifiers. The on-wafer measurement results show that the average small-signal gain of the power amplifier is 18 dB. The power test results show that the saturated output power of the power amplifier is better than15.8 mW from 210 GHz to 230 GHz, with a maximum output power of 20.9 mW at 223 GHz. The size of the TMIC chip is 2.18 mm×2.40 mm.