Patent ID: 7135738

Claim:
A trench-gated MOSFET formed in a semiconductor substrate of a first conductivity type, the substrate not comprising an epitaxial layer, the trench-gated MOSFET comprising: at least four trenches formed at a surface of the substrate, a first trench being separated from a second trench by a first drain mesa, the second trench being separated from a third trench by a source mesa, and the third trench being separated from a fourth trench by a second drain mesa; the source mesa comprising: a source region of a second conductivity type opposite to the first conductivity type adjacent a surface of the substrate, the source region having a first doping concentration of the second conductivity type; a body region of the first conductivity type adjacent the source region and extending across the second mesa, the body region having a junction depth deeper than the source region; and a high voltage drift region adjacent the body region and extending across the source mesa, the high voltage drift region having a second doping concentration of the second conductivity type; each of the drain mesas comprising: a drain region of the second conductivity adjacent a surface of the substrate and extending entirely across the first and second drain mesas, respectively, the drain region having a third doping concentration of the second conductivity type; and a low voltage well of the second conductivity type adjacent the drain region and extending entirely across the drain mesas, respectively, the low voltage well having a fourth doping concentration of the second conductivity type; and a high voltage well of the second conductivity type, the high voltage well abutting the low voltage well in each of the drain mesas and the high voltage drift region, the high voltage well extending below a bottom of each of at least the second and third trenches; wherein the first doping concentration is greater than the second doping concentration and the third doping concentration is greater than the fourth doping concentration.