An accumulation layer has a function of reducing an ON voltage (Von), which is a voltage between the collector and the emitter when turning on the IGBT, by accumulating carrier. However, when turning off the IGBT, the carrier contributes to a turn-off loss (Eoff). A semiconductor device is provided, comprising: a semiconductor substrate, wherein the semiconductor substrate includes: trench portions, a mesa portion each provided between two adjacent trench portions, and a drift layer, wherein the trench portions include: a gate trench portion, and a dummy trench portion, wherein the mesa portion has: an emitter region, a contact region, and a accumulation layer, wherein the number of accumulation layers provided in a depth direction in the mesa portion adjacent to the gate trench portion is larger than that of the accumulation layers provided in the depth direction in the mesa portion between the two dummy trench portions.