This letter presents an integrated power amplifier (PA), with high linearity and efficiency, which uses a passive four-way power distribution network to increase the maximum output levels. The gain unit consists of a differential preamplifier and power stage, interfaced by passive baluns at the input and output. The circuit is intended for ultrawideband mm-wave communication systems operating around 180 GHz. It exhibits a gain of 19 dB, with low ripple and group delay variation, over a large bandwidth of 80 GHz. The 1-dB compression point and the saturated output power occur around 13 and 15 dBm, respectively. The maximum dc power consumption is 830 mW and results in a power-added efficiency of up to 3.5%. The final chip occupies an area of 0.92 mm² and is implemented in a 130-nm SiGe BiCMOS process, which offers a maximum oscillation frequency fmax of 450 GHz. To the best of authors' knowledge, this circuit demonstrates one of the largest bandwidths, in combination with the highest output power and best linearity, of any silicon-based PA operating above 200 GHz.