Anodic oxidation was performed to 4H-SiC in order to suppress the negative impacts on the Schottky diode characteristics. The electrochemical deposition of ZnO before and after the oxidation revealed a reduction in the number of areas with low Schottky barrier height. Before and after the oxidation, current-voltage characteristics of Ni Schottky contacts was compared, and it was found out that the characteristics were improved after the oxidation. These results suggest that the anodic oxidation is a promising technique to suppress the negative influence of the crystal defects.