A method of manufacturing a silicon carbide semiconductor device having a MOS structure includes preparing a substrate (1) made of silicon carbide, and forming a channel region (4), a first impurity region (6, 7), a second impurity region (1, 13), a gate insulation layer (8), and a gate electrode (9) to form a semiconductor element on the substrate. In addition, a film is formed on the semiconductor element to provide a material of an interlayer insulation layer (10), and a reflow process is performed at a temperature about 700 DEG C. or over in an wet atmosphere so that the interlayer insulation layer is formed from the film and an edge portion of the gate electrode is rounded and oxidized.