An inventive semiconductor device includes a semiconductor layer, a source region provided in a surface layer portion of the semiconductor layer, a drain region provided in the surface of the semiconductor layer in spaced relation from the source region, a gate insulation film provided in opposed relation to a portion of the surface of the semiconductor layer present between the source region and the drain region, a gate electrode provided on the gate insulation film, and a drain-gate isolation portion provided between the drain region and the gate insulation film for isolating the drain region and the gate insulation film from each other in non-contact relation.