A semiconductor device comprises an SOI substrate formed with a mono-crystalline semiconductor layer through an embedded insulating layer on a first conductivity type semiconductor substrate; a MIS type field-effect transistor provided within a device region defined by isolating said mono-crystalline semiconductor layer with a device isolation region and having a gate electrode; an opening formed penetrating said device isolation region and said embedded insulating layer and reaching said semiconductor substrate; and a substrate electrode provided covering said opening and taken out up to the surface flush with said gate electrode. And a method of manufacturing a semiconductor device, comprises providing a device isolation region for defining a device region on a mono-crystalline semiconductor layer of an SOI substrate formed with a mono-crystalline semiconductor layer through an embedded insulation payer on a semiconductor substrate of a first conductivity type; forming an opening penetrating said device isolation region and said embedded insulation layer and reaching said semiconductor substrate; depositing polysilicon on said SOI substrate and within said opening and providing a gate electrode and a substrate electrode of said MIS type field-effect transistor by executing the patterning thereon; and implanting impurities into said gate electrode and said substrate electrode.