Nitrided layers were grown on a 4H-SiC(0001) by plasma nitridation method using NH 3 . Nitridation was enhanced with increasing RF power and with decreasing growth pressure. However, the exact capacitance-voltage (C-V) properties of the nitride layer/SiC interface could not be determined because of the leakage current. The SiO 2 film was deposited on the nitrided layer by thermal chemical vapor deposition method using tetraethoxysilane (TEOS) omit obtain an insulating film with sufficient thickness and an exact interface property. The interface state density D it was evaluated from C-V characteristics by the Terman method. It was indicated that D it near the mid gap of the TEOS oxide/nitride layer structure was higher than those of the TEOS-SiO 2 films and thermal oxide film. The D it of the oxide/nitride layer successfully decreased by post NH 3 annealing.