A semiconductor device having an IGBT includes: a substrate; a drift layer and a base layer on the substrate; trenches penetrating the base layer to divide the base layer into base parts; an emitter region in one base part; a gate element in the trenches; an emitter electrode; and a collector electrode. The one base part provides a channel layer, and another base part provides a float layer having no emitter region. The gate element includes a gate electrode next to the channel layer and a dummy gate electrode next to the float layer. The float layer includes a first float layer adjacent to the channel layer and a second float layer apart from the channel layer. The dummy gate electrode and the first float layer are coupled with a first float wiring on the base layer. The dummy gate electrode is isolated from the second float layer.