Increased voltage MOS semiconductor device

Claim 1

An increased operating voltage metal-oxide semiconductor device comprising: a source area of a first conductivity type semiconductor material connected to a source electrode; a drain area, with extended length of first conductivity type semiconductor material; an emitter area of a second conductivity type semiconductor material, contiguous to said drain area, said emitter area connected to an emitter electrode; a second conductivity type semiconductor material between said source and drain areas, including a channel forming area within a surface layer of said material; a gate insulating film, over said channel forming area, which extends over the drain area, said film having a first portion near the channel forming area and a second portion thicker near the emitter electrode; a gate electrode over said gate insulating film and including a portion extended over said second portion of the gate insulating film; and a relaxation area of second conductivity type semiconductor material within said drain area immediately below a juncture between said first and second portions of the gate insulating film and not extended laterally beyond said gate electrode; whereby the relaxation area and the gate portion extended over said second portion permits a greater operating voltage without breakdown by preventing an excess field concentration from existing in said drain area immediately below a juncture between said first and second portions of the gate insulating film.