Patent ID: 8247868

Claim:
A power MOSFET, comprising: a substrate; an epitaxial layer with lower concentration dopants of a first conduction type, formed on the substrate; a first trench having an inner wall, extending downward from a first region of a top surface of the epitaxial layer, and a first gate dielectric layer and a gate region composed of a conductive material being formed in the first trench, wherein the first gate dielectric layer is sandwiched between the inner wall of the first trench and the gate region; a second trench, extending downward from a bottom of the first trench with a second gate dielectric layer being formed in the second trench, wherein the second trench is smaller than the first trench in width; a calabash-shaped first well doped with dopants of a second conduction type, extending from the bottom of the first trench to and beyond the bottom of the second trench, and surrounding a sidewall and the bottom of the second trench, wherein the second conduction type is opposite to the first conduction type; a second well with dopants of the second conduction type, extending downward from a second region of the top surface of the epitaxial layer, wherein the second well and the first well are separated from each other; and a source region with dopants of the first conduction type located within the second well.