This paper discusses the issues regarding reliability of large-area (up to 9mm2) gate oxide on the C-face of 4H-SiC. We first show that the initial failure in TDDB characteristics of large area gate oxide is strongly correlated with the surface-defect density. Using wafers with low surface-defect density wafers, scaling analysis of the area-dependence of TDDB characteristics has been performed. It has shown that the reliability of a large area gate oxide is dominated by initial and random failures. Further, we have shown that, by optimizing the temperatures of post-oxidation anneal in hydrogen atmosphere, the random failures of TDDB characteristics are substantially reduced.