An N-channel MOS field-effect transistor on an SOI substrate including a source electrode, drain and gate electrodes both disposed via a field oxide film, a gate oxide film, a high concentration P-type layer, a high concentration N-type layer contacting the source electrode and the gate oxide film, a high concentration N-type layer contacting the drain electrode, a p-body layer contacting the high concentration P-type and N-type layers and the gate oxide film. In this transistor, an N-type layer with a concentration higher than that of a drain region contacting the p-body layer constitutes a region covering at most 95% of the source-drain distance. Further, an N-type region having a concentration from 3×1016/cm3 to 1×1022/cm3 is provided near a buried oxide film under the drain electrode.