We fabricated a p+/n-/n+ 4H-SiC IMPATT diode with guard-ring termination. The p+ -
layer and the guard-ring were formed by ion implantation. The diode showed abrupt avalanche breakdown characteristics and we obtained a peak output power of 1.8 W at 11.93 GHz, which is the highest peak output power ever for the SiC IMPATT diodes in X-band.