Semiconductor device and its manufacture

A conventional power MOSFET prevents inversion of peripheral surface with wide width annular and shield metal, which however enlarges the area of peripheral region and restricts the increase of the area of element region. On the other hand, this invention provides an inversion preventing region of MIS (MOS) structure. The width of the inversion preventing region can be only the width of polysilicon and the area of oxide film can be increase in the depth direction of trench. Accordingly, the leak current can be reduced even the area of peripheral region is not made widely, and the ON resistance of MOSFET can also be reduced since the element region is enlarged.