Field effect transistor with insulated gate electrode

A field effect transistor with insulated gate electrode having a semiconductor body, said semiconductor body having first and second surfaces, oppositely located, comprising:

• an island-shaped first region of a first conductivity type which adjoins said first surface;
• a first zone of the second conductivity type within said island shaped first region and likewise adjoining said first surface;
• a second region of the second conductivity type which surrounds said first region and forms a pn junction therewith and adjoins said oppositely located second surface;
• a groove in said first surface and extending through said first zone and said first region into said second region;
• the wall of said groove being coated with an electrically insulating layer;
• a gate electrode on said layer;
• said first zone and said second region being provided with connection conductors associated with the source and drain electrodes of said field effect transistor;
• a third region of said second conductivity type extending from said first surface to said second region;
• said first region forming with said underlying second region a first pn junction extending substantially parallel to said first surface and bounded laterally at least partly by said third region of the second conductivity type which extends from the first surface down to the second region and forms with the first region a second pn junction having a lower breakdown voltage than said first pn junction;
• a fourth region of said first conductivity type adjoining said first surface present in said first region separating said first region and said first zone from each other and having a higher doping concentration than the first region;
• and
• the doping concentration and the thickness of said first region being so small that when applying a voltage in reverse direction between said first and said second regions, the depletion zone of said transistor extends from said first pn junction up to said first surface throughout the thickness of said first region at a voltage which is lower than the breakdown voltage of said second pn junction.