A semiconductor device includes a lateral switching device having: a substrate; a channel forming layer that has a heterojunction structure made of a GaN layer and an AlGaN layer and is formed with a recessed portion, on the substrate; a gate structure part that includes a gate insulating film and a gate electrode formed in the recessed portion; and a source electrode and a drain electrode on opposite sides of the gate structure part on the channel forming layer. The AlGaN layer includes a first AlGaN layer that has an Al mixed crystal ratio determining a two dimensional electron gas density, and a second AlGaN layer that has an Al mixed crystal ratio smaller than that of the first AlGaN layer to induce negative fixed charge, and is disposed in contact with the gate structure part and spaced from the source electrode and the drain electrode.