In a semiconductor device, a trench gate has a bottom portion in a drift layer and a communication portion extending from a surface of a base layer to communicate with the bottom portion. A distance between adjacent bottom portions is smaller than a distance between adjacent communication portions in a x-direction. A region between adjacent trench gates is divided in a y-direction into an effective region as an electron injection source and an ineffective region which does not serve as the electron injection source. An interval L1 (>0) of the ineffective region in the y-direction, a length D1 of the communication portion in the z-direction, and a length D2 of the bottom portion in the z-direction satisfy L1≦2(D1+D2). The z-direction is orthogonal to a x-y plane defined by the x-direction and the y-direction which are orthogonal to each other.