Patent ID: 6878992

Claim:
A power MOSFET, comprising: a low resistive semiconductor substrate of a first conductivity type having a first main surface and a second main surface opposing to each other; a drift layer of the first conductivity type formed on the first main surface of the semiconductor substrate; a high resistive epitaxial layer of the first conductivity type formed on the drift layer; trenches formed in the epitaxial layer and the drift layer to extend from a surface of the epitaxial layer into the drift layer, the trenches having bottom portions surrounded by the drift layer; gate electrodes buried in the trenches with gate insulating films interposed between walls of the trenches and the gate electrodes; first and second low resistive source layers of the first conductivity type formed in a surface region of the epitaxial layer adjacent to the gate insulating films; a low resistive base layer of a second conductivity type formed in the surface region of the epitaxial layer between the first and second source layers; a source electrode electrically and commonly connected to the source layers and the base layer; and a drain electrode electrically connected to the second main surface of the semiconductor substrate, wherein the drift layer has an impurity concentration higher than that of the epitaxial layer and the epitaxial layer intervening between the trenches is depleted in a case where no voltage is applied between the source electrode and the gate electrodes.