In this work, it was clarified that many dislocations present on the substrate surface markedly deteriorated the TDDB property of thermal gate oxide on commercially purchased 4H-SiC epitaxial substrates. However, it was also experimentally shown that even after removing all of the dislocations, there was still a significant difference in the charge-to-breakdown (QBD) value between thermal oxides on SiC and on Si. It was suggested that this difference might partly originate from the intrinsic physics. The ONO gate dielectric was shown to be a promising alternative to thermal oxide. Experimental results indicate that the ONO dielectric on 4H-SiC could achieve a higher QBD value than thermal oxide on Si. A value of QBD = 408 C/cm2 was achieved for an ONO gate dielectric, with a SiO2 equivalent thickness of 40 nm, on regular 4H-SiC.