A wide band gap semiconductor device includes a semiconductor layer, a trench formed in the semiconductor layer, first, second, and third regions having particular conductivity types and defining sides of the trench, and a first electrode embedded inside an insulating film in the trench. The second region integrally includes a first portion arranged closer to a first surface of the semiconductor layer than to a bottom surface of the trench, and a second portion projecting from the first portion toward a second surface of the semiconductor layer to a depth below a bottom surface of the trench. The second portion of the second region defines a boundary surface with the third region, the boundary region being at an incline with respect to the first surface of the semiconductor layer.