A semiconductor device includes first and second electrodes, a semiconductor part therebetween, and first and second control electrodes in a trench of the semiconductor part. The first and second control electrodes are arranged along a front surface of the semiconductor part. The semiconductor part includes first and third layers of a first-conductivity-type, and the second and fourth layer of a second-conductivity-type. The second layer is provided between the first layer and the second electrode. Between the second layer and the second electrode, the third and fourth layers are provided apart from the first layer with first and second portions of the second layer interposed, respectively. The first portion of the second layer has a first thickness in a second direction from the first electrode toward the second electrode. The second portion of the second layer has a second thickness in the second direction larger than the first thickness.