The semiconductor device comprises a semiconductor layer 18 formed on an insulation layer 16, a gate electrode 22 formed on the semiconductor layer with a gate insulation film 20 formed therebetween, a source/drain region 24 formed on the semiconductor layer on both sides of the gate electrode, and a semiconductor region 14 buried in the insulation layer 16 in a region below the gate electrode. The surface scattering of the carriers and phonon scattering can be prevented while suppressing the short channel effect. Resultantly the semiconductor device can have high mobility and high speed.