A semiconductor device includes; a semiconductor substrate; an emitter electrode provided on the semiconductor substrate; a gate electrode provided on the semiconductor substrate; a drift layer of a first conduction type provided in the semiconductor substrate; a source layer of the first conduction type provided on an upper surface side of the semiconductor substrate; a base layer of a second conduction type provided on the upper surface side of the semiconductor substrate; a collector electrode provided below the semiconductor substrate; and a two-part dummy active trench including, at an upper part, an upper dummy part not connected with the gate electrode and including, at a lower part, a lower active part connected with the gate electrode and covered by an insulating film, in a trench of the semiconductor substrate, wherein a longitudinal length of the lower active part is larger than a width of the lower active part.