A first SiO.sub.2 thin film, a tungsten gate electrode, and a second SiO.sub.2 thin film are selectively formed on a first n.sup.+-type GaN contact semiconductor layer in that order and in a multilayer film structure having the three layers, a stripe-shaped opening is formed. Via the opening, an undoped GaN channel semiconductor layer and the second n.sup.+-type GaN contact semiconductor layer are formed so that both the layers are regrown by, for example, metal organic chemical vapor deposition. A source electrode and a drain electrode are formed so as to contact the corresponding second and first n.sup.+-type GaN contact semiconductor layers. The regrown undoped GaN channel semiconductor layer and the regrown second n.sup.+-type GaN contact semiconductor layer are horizontally grown portions and hence, the contact area of the electrode can be made larger than the area of the opening.