A silicon nitride film having a thickness in a range from 1 [nm] to 3 [nm] is deposited on a front surface of a silicon carbide semiconductor base, by an ALD method. Next, on the silicon nitride film, for example, a silicon oxide film having a thickness in a range from 20 [nm] to 100 [nm] is deposited. After deposition of the silicon oxide film, for example, heat treatment is performed at a temperature in a range from 1100 degrees C. to 1350 degrees C., in a gas atmosphere that includes oxygen. By this heat treatment, nitrogen surface density of an interface of the silicon carbide semiconductor base and the silicon oxide film (gate insulating film) is increased, reducing interface state density of the interface of the silicon carbide semiconductor base and the silicon nitride film.