This work demonstrates the first analog linearization of a 300-GHz solid-state power amplifier in 35-nm InGaAs metamorphic HEMT technology. The PA module uses a single class-C stage as a predistorter to counteract gain and phase compression of the main amplifier, and the large-signal phase behavior of class-C biased amplifiers is characterized at submillimeter-wave frequencies for the first time. At optimum bias, the predistorter improves the output-referred 1-dB compression point of the main amplifier by 1.3–3 dB across 280–317.5 GHz and shifts the 1◦ phase-compression point by 2.9 dB at 295 GHz. The predistorter reduces error vector magnitude 0.9% and improves adjacent channel power ratio by 7.2 dB under low-drive conditions at 295 GHz with 1.35 GHz modulated bandwidth.