Methods are provided for improving inversion layer mobility and providing low defect density in a semiconductor device based upon a silicon carbide (SiC) substrate. More specifically, embodiments of the present method provide for the formation of a gate oxide on a silicon carbide substrate comprising oxidizing the substrate with a gaseous mixture comprising oxygen at a temperature of at least about 1300° C. Semiconductor devices, such as MOSFETS, based upon a substrate treated according to the present method are expected to have inversion layer mobilities of at least about 12 cm2/Vs.