A gate insulating film which is an oxide layer mainly made of SiO 2 is formed over a silicon carbide substrate by thermal oxidation, and then, a resultant structure is annealed in an inert gas atmosphere in a chamber. Thereafter, the silicon carbide-oxide layered structure is placed in a chamber which has a vacuum pump and exposed to a reduced pressure NO gas atmosphere at a high temperature higher than 1100°C and lower than 1250°C, whereby nitrogen is diffused in the gate insulating film. As a result, a gate insulating film which is a V-group element containing oxide layer, the lower part of which includes a high nitrogen concentration region, and the relative dielectric constant of which is 3.0 or higher, is obtained. The interface state density of an interface region between the V-group element containing oxide layer and the silicon carbide layer decreases.