The electron-hole transport including impact ionization and millimeter wave power generation in 4H-SiC has been studied by the Monte Carlo Particle technique. The model of 4H-SiC consists of three electron and two hole bands. The millimeter wave power generation is investigated in p(+)-n-n(-)-n(+) 4H-SiC IMPATT diodes operating in parallel resonant circuit. It will be shown that 4H-SiC offers the potential to generate millimeter wave power over several watts at around 200 GHz.