Switching loss is reduced. A first surface of a semiconductor substrate has a portion included in an IGBT region and a portion included in a diode region. Trenches formed in the first surface include a gate trench and a boundary trench disposed between the gate trench and the diode region. A fourth layer of the semiconductor substrate is provided on the first surface and has a portion included in the diode region. The fourth layer includes a trench-covering well region that covers the deepest part of the boundary trench, a plurality of isolated well regions, and a diffusion region that connects the trench-covering well region and the isolated well regions. The diffusion region has a lower impurity concentration than that of the isolated well regions. A first electrode is in contact with the isolated well regions and away from the diffusion region.