A semiconductor device (1) has a substrate (10), a gate-insulating film (20), and a gate electrode (30). The substrate (10) comprises a compound semiconductor, and has recesses (17) formed therein which have sidewall surfaces (17A) and open to one principal surface (10A), when viewed from a cross-section in the thickness direction. The gate-insulating film is positioned so as to contact the top of the sidewall surfaces (17A). The gate electrode (30) is positioned so as to contact the top of the gate-insulating film (20). The substrate (10) includes: first-conductive-type source regions (15) positioned so as to be exposed on the sidewall surfaces (17A); and second-conductive-type body regions (14) positioned opposite the one principal surface (10A) when seen from the source regions (15), in contact with the source regions (15), and exposed on the sidewall surfaces (17A). The recesses (17) have a closed shape when seen from a planar view, and the sidewall surfaces (17A) have a convex shape in an outward direction in all directions, when seen from an arbitrary position inside the recesses (17). As a result, it is possible to provide a semiconductor device (1) capable of improving voltage resistance.