Reliability of the gate oxide is influenced by the device structure and the processes. In the SiC MOSFET, the surface morphology is degraded by the high temperature activation RTA, and the degradation is remarkable on the n+ source region. This study develops the method to suppress the degradation of the reliability of the gate oxide on the carbon face. By utilizing the carbon cap for the RTA and the high density O2 plasma etching to remove the carbon cap, the reliability is drastically improved both on the un-implanted and the implanted surfaces. Especially, the degradation of the reliability is perfectly suppressed on the un-implanted surface.