In a semiconductor device, an edge termination region which surrounds an active region includes an electric field reduction mechanism including guard rings, first field plates which come into contact with the guard rings, and second field plates which are provided on the first field plates, with an interlayer insulating film interposed therebetween. The factor is determined from an initial strength characteristic ascertained from a non-aged piece of airbag fabric and a final strength characteristic ascertained from an artificially aged piece of airbag fabric. The blunting of the edges and corners of the metallization by level embedding of the entire metallized insulating element improves the insulating property of semiconductor module in the area of the critical electrical field region.