We report high-power modified uni-traveling carrier photodiodes with 150-GHz bandwidth. To improve the RF output power, the photodiode chips are flip-chip bonded on diamond submounts with high thermal conductivity to enhance heat dissipation. Measured 3-dB bandwidths of 4-μm, 6-μm, 8-μm, and 10-μm diameter photodiodes reach 150 GHz, 129 GHz, 117 GHz, and 105 GHz, respectively. RF output power with 12.7 dBm at 90 GHz, 11.3 dBm at 100 GHz, 8.5 dBm at 110 GHz, -3 dBm at 150GHz, and -5.7 dBm at 165GHz are achieved.