A semiconductor device reduces the on-resistance and, at the same time, raises the breakdown voltage. The drain electrode 20 of the semiconductor device runs through cap layer 13 and electron supply layer 12 and gets to a position lower than two-dimensional electron gas layer 14 in channel layer 11. Thus, the drain electrode 20 directly contacts the channel layer 11, the electron supply layer 12 and the cap layer 13. Angles (acute angles) θ, ø and ψ are formed by the drain electrode 20 and the channel layer 11, the electron supply layer 12 and the cap layer 13 as viewed in the direction in which a hetero interface is formed (the transverse direction in FIG. 1) and relationships of ø