A semiconductor device is provided which is capable of removing the heavy metal impurity in a SOI layer by gettering, and realizing an improvement in breakdown voltage and reliability. The semiconductor device comprises polysilicon regions functioning as a gettering site, which are selectively formed in a buried fashion, such as to make no contact with a gate insulating film and an element isolation insulating film, in a main surface of part of a SOI layer where a drain region and a source region are disposed; and contact holes being filled with polysilicon plug functioning as a gettering site, and extending through an interlayer insulating film between an upper surface of the interlayer insulating film and an upper surface of the polysilicon regions.