A silicon carbide semiconductor device fabrication method comprises: forming a drift layer (2) upon a silicon carbide substrate (1); forming a base layer (3) upon either the drift layer (2) or an obverse layer part thereof; forming a source region (4) upon the surface layer part of the base layer (3); forming a trench (6) which passes through the base layer (3) and reaches the drift layer (2); forming a gate electrode (8) within the trench (6) upon a gate insulation film (7); forming a source electrode (9) which is electrically connected to the source region (4) and the base layer (3); and forming a drain electrode (11) upon the rear face side of the substrate (1). The forming of the trench (6) further comprises: flattening a substrate surface; and etching to form the trench (6) after flattening.