Two high power communication amplifiers operating in the Extremely High Frequency (EHF) spectrum are described. Both amplifiers are based on silicon double-drift IMPATT diodes for power generation. The first amplifier operates in the high gain, narrowband injection-locking mode and represents a first step toward low cost manufacturing of this type of amplifier. It is capable of 6.2 W and 31 dB gain at 36.79 GHz, with 250 MHz injection-locking bandwidth. The second amplifier operates in the low gain, wideband negative resistance mode in which there is no power output in the absence of an input signal. A state-of-the-art power output in excess of 3.5 W was achieved from 43.5 to 44.5 GHz with a nominal 3 dB gain. This amplifier is in its advanced development stage.