The reliability of CVD gate oxide was investigated by CCS-TDDB measurement and compared with thermally grown gate oxide. Although the QBD of thermal oxide becomes smaller for the larger oxide area, the QBD of CVD oxide is almost independent of the investigated gate oxide area. The QBD at F = 50% of CVD oxide, 3 C/cm2, is two orders of magnitude larger for the area of 1.96×10-3 cm2 at 1 mA/cm2 compared to that of thermal oxide. More than 80% of the CVD oxide breakdown occurs at the field oxide edge and more than 70% of the thermal oxide breakdown in the inner gate area. These results suggest that the lifetime of CVD oxide is hardly influenced by the quality of SiC, while the defects and/or impurities in SiC affect the lifetime of thermally grown oxide.