Insulated gate silicon carbide semiconductor device and a manufacturing method thereof

A relaxed electric field of the gate insulating film, the increase in on-resistance can be suppressed, providing an insulated gate silicon carbide semiconductor device and a manufacturing method thereof. A first conductivity type drift layer 2a on the silicon carbide substrate 1 of the 4H type having a major surface greater than 0 ° off-angle in the off direction is provided from the {0001} plane, a surface layer of the drift layer 2a a first base region 3 of the second conductivity type on the side, and the source region 4 of the first conductivity type, a trench 5, a gate insulating film 6 formed in the trench, the drift layer in contact with the bottom of the trench 5 a protective diffusion layer 13 of the second conductivity type provided in the 2a, to connect the protective diffusion layer 13 of the first base region 13, at least one trench side walls of the plurality of trenches side wall at least a parts to provided in contact comprises a second base region 14 of the second conductivity type bottom is less than the depth of the bottom surface of the protective diffusion layer 13, a. .The