Exposure of a gate conductive film covered by an interlayer insulation film in a unit cell portion is reduced when a gate contact region is formed. A method of manufacturing a semiconductor device includes forming a gate conductive film to come in contact with a gate oxide film in a unit cell portion, forming a gate wire to come in contact with the gate oxide film in a termination region, forming a first insulation film on an upper surface of the gate wire in the termination region, subjecting an upper surface of the gate conductive film in the unit cell portion to thermal oxidation with use of the first insulation film as a mask to form a thermal oxide film on the upper surface of the gate conductive film, and forming a second insulation film covering the first insulation film and the thermal oxide film.