Semiconductor device and its fabrication method

Claim 1

A semiconductor device comprising: a first semiconductor region of a first conductivity type formed on an insulating substrate; an insulating layer formed in contact with said first semiconductor region at a side opposite to said insulating substrate; a control electrode arranged on said first semiconductor region sandwiching said insulating layer therebetween; second and third semiconductor regions adjacent to and sandwiching said first semiconductor region; and first, second and third electrodes connected respectively to said first, second and third semiconductor regions; wherein potentials of said second and third electrodes and said control electrode are regulated for converting the current flowing from said second semiconductor region through said first semiconductor region into said third semiconductor region, characterized in that a thickness of said insulating layer, a material of said control electrode, an impurity concentration of said first semiconductor region and a thickness of said first semiconductor region are determined so that, under a condition that said first, second and third electrodes and said control electrode are maintained at the same potential, said first semiconductor region is depleted, and a surface of said first semiconductor region in contact with said insulating layer is at a weakly inverted state, and in that said control electrode and said third electrode connected to said first semiconductor region are at the same potential when a driving potential is applied thereto.