SiO2/SiC interface was investigated by using super-higher-order (SHO) scanning nonlinear dielectric microscopy (SNDM) with high spatial resolution. Comparison of non-oxidized and thermally oxidized 4H-SiC wafer (Si-face) revealed that only 5 min oxidation makes the interface quality spatially inhomogeneous. Next four SiC wafers treated under different post oxidation annealing (POA) conditions in NO ambient (three “with” and one “without” POA) were also compared. Using SHO-SNDM, local capacitance-voltage (C-V) curves were obtained. The local C-V curve obtained in sample with POA was more close to ideal C-V curve compared to the C-V curves obtained in the sample without POA. In addition, two-dimensional normalized SNDM images taken on the four SiC wafers were observed, which showed that the spatial deviation of interface state was reduced by the POA treatment. Moreover, standard deviations σ of the normalized SNDM images were calculated. Then, very strong correlations between σ and interface-state density Dit as well as channel electron mobility μFE were observed.