The present invention provides a semiconductor device capable of suppressing current collapse, and also of preventing dielectric breakdown voltage and gain from lowering so as to perform high-voltage operation and realize an ideal high output. On a substrate (101), there are formed a buffer layer (102) made of a first GaN-based semiconductor, a carrier traveling layer (103) made of a second GaN-based semiconductor and a carrier supplying layer (104) made of a third GaN-based semiconductor. A recess structure (108) is made by eliminating a part of a first insulation film (107) and a part of the carrier supplying layer (104). Next, a gate insulation film (109) is deposited, and then a gate electrode (110) is formed so as to fill up the recess portion (108) and cover on over an area where the first insulation film (107) remains so that its portion on the drain electrode side is longer than that on the source electrode side. Such a recess structure is employed so as to provide the high-output semiconductor device capable of performing the high-voltage operation.