A silicon carbide semiconductor device includes a silicon carbide semiconductor substrate of a first conductivity type, a first silicon carbide semiconductor layer of the first conductivity type, a second silicon carbide semiconductor layer of a second conductivity type, a first silicon carbide semiconductor region of the first conductivity type, a trench, and a gate electrode on a gate insulating film. Between the gate insulating film and any one among the first silicon carbide semiconductor layer, the second silicon carbide semiconductor layer, and the first silicon carbide semiconductor region is an interface section where a concentration of oxygen varies, the interface section having closer to the gate insulating film than to the any one among the first silicon carbide semiconductor layer, the second silicon carbide semiconductor layer, and the first silicon carbide semiconductor region, a region where a rate of increase of the oxygen included in the interface section is greatest.