A semiconductor device comprising: a substrate made of a compound semiconductor and having a recess, which opens at one main surface thereof and has side wall surfaces; a gate insulating film disposed on and in contact with each of said side wall surfaces; and a gate electrode disposed on and in contact with said gate insulating film, said substrate including a source region having first conductivity type and disposed to be exposed at said side wall surface, when viewed in a cross section along a thickness direction, and a body region having second conductivity type and disposed in contact with said source region at a side opposite to said one main surface so as to be exposed at said side wall surface, when viewed from said source region, characterised in that: said recess has a closed hexagonal shape when viewed in a plan view, said source region is provided to surround said recess, when viewed in a plan view, two adjacent side wall surfaces form an angle smaller than 180° when viewed from an arbitrary location in said recess, wherein said side wall surface of the recess microscopically includes a first plane having a plane orientation of and a second plane S2 having a plane orientation of, and the first plane S1 and the second plane S2 are periodically repeated, thereby forming a combined plane SR having a plane orientation of, wherein microscopically means minutely to such an extent that at least the size about twice as large as an interatomic spacing is considered. a substrate made of a compound semiconductor and having a recess, which opens at one main surface thereof and has side wall surfaces; a gate insulating film disposed on and in contact with each of said side wall surfaces; and a gate electrode disposed on and in contact with said gate insulating film, said substrate including a source region having first conductivity type and disposed to be exposed at said side wall surface, when viewed in a cross section along a thickness direction, and a body region having second conductivity type and disposed in contact with said source region at a side opposite to said one main surface so as to be exposed at said side wall surface, when viewed from said source region, characterised in that: said recess has a closed hexagonal shape when viewed in a plan view, said source region is provided to surround said recess, when viewed in a plan view, two adjacent side wall surfaces form an angle smaller than 180° when viewed from an arbitrary location in said recess, wherein said side wall surface of the recess microscopically includes a first plane having a plane orientation of and a second plane S2 having a plane orientation of, and the first plane S1 and the second plane S2 are periodically repeated, thereby forming a combined plane SR having a plane orientation of, wherein microscopically means minutely to such an extent that at least the size about twice as large as an interatomic spacing is considered. said recess has a closed hexagonal shape when viewed in a plan view, said source region is provided to surround said recess, when viewed in a plan view, two adjacent side wall surfaces form an angle smaller than 180° when viewed from an arbitrary location in said recess, wherein said side wall surface of the recess microscopically includes a first plane having a plane orientation of and a second plane S2 having a plane orientation of, and the first plane S1 and the second plane S2 are periodically repeated, thereby forming a combined plane SR having a plane orientation of, wherein microscopically means minutely to such an extent that at least the size about twice as large as an interatomic spacing is considered.