The MOSFET includes a semiconductor (p+Si) substrate (10) and several (p+) protective ring layers to guarantee a high withstanding voltage. A deep (p ) layer (16) is formed and serves as part of the base-diffusion layer (22) in which a flat (p+) layer (24) is produced, and the base-diffusion layer (22) is used as a mask to generate the gate-electrode (20). The (n+) source diffusion layer (26) is also used as a mask in forming the gate-electrode (20), which is produced on the gate insulation layer (18).The source electrode (30) is formed from the contact well in the Vapour diffusion (CVD) Si02 layer on the surface, and the drain electrode (32) is formed on the bottom of the substrate (10)
