A semiconductor device includes: a gate electrode that is provided on a semiconductor layer; a source electrode and a drain electrode that are provided on the semiconductor layer so as to interpose the gate electrode; a source wall that extends from the source electrode to a point between the gate electrode and the drain electrode through the region above the gate electrode, the source wall having a joining portion in the extending region; and an electrode portion that is joined to the joining portion and has a region extending closer to the drain electrode than the joining portion.