A method for manufacturing a silicon carbide semiconductor device includes: preparing a silicon carbide single crystal substrate having a flatness with an average roughness of 0.2 nm or less; gas-etching a surface of the silicon carbide single crystal substrate under an atmosphere of a reducing gas; and forming a silicon carbide layer on the gas-etched surface of the silicon carbide single crystal substrate, wherein an etching rate of the gas etching is made in a range of 0.5 μm/hour or faster to 2.0 μm/hour or slower.