High-efficiency and broadband power amplifiers (PAs) are key to enabling the next-generation of millimeter-Wave (mm-Wave) systems and multi-functional communication, sensing and imaging arrays. Due to the low f/fmax, low breakdown voltages and low gain in silicon devices at mm-Wave frequencies, InP HBTs have been promising candidates to enable high-efficiency, high power and broadband transmitter frontends for compact phased and MIMO arrays above 50 GHz. In this paper, we present two broadband PA architectures covering 50-70 GHz, and 64-110 GHz in 250 nm InP HBT process through specially designed asymmetrical power combining architectures with stacked PA cells. The PAs generate more than 20 dBm of peak power in both the bands with peak output collector efficiency (ηout) exceeding 40%, total collector efficiency (η) exceeding 30% and peak power added efficiency (PAE) >23 % for both bands. This work presents one of the highest bandwidth and highest efficiency PAs with peak power greater than 20 dBm.