We have observed the SiO(2)/SiC interfaces formed on 3.5 degrees and 8 degrees off-angle 6H-SiC (0001) and 8 degrees off-angle 4H-SiC (0001) substrates using transmission electron microscopy (TEM). The step structures were observed even after the oxidation. It was found that the number of SI-C bilayer at the steps increased and the roughness of SiO(2)/SiC interface became large as the off-angle increased. Therefore, it is considered that one of the reasons for lower channel mobility for 4H-SiC MOSFETs fabricated on 8 degrees off-angle SiC substrate is due to rougher SiO(2)/SiC interface compared to 6H-SiC h MOSFETs fabricated on 3.5 degrees off-angle SiC substrate.