Abstract: A vertical power field effect transistor is liable to be destroyed due to a large amount of current backwardly flowing from the drain region through the base region into the source region when a parasitic bipolar transistor fabricated therefrom turns on, and base contacts radially and inwardly project from the four corners a rectangular base region into a rectangular source region so that the resistance of the base region is decreased, thereby effectively preventing the parasitic bipolar transistor from turn-on.

Abstract: A power semiconductor device is constructed by integrating a DMOS transistor and a lateral MOS transistor on the same semiconductor chip. The lateral MOS transistor is formed within a well with a conductivity type which is the same as the conductivity type of the source region of the DMOS transistor. The gate voltage is monitored at the time of connecting the gate and the drain of the lateral MOS transistor and of driving it at a constant current. When the gate voltage drops below a predetermined value, the driving of the DMOS transistor is stopped. The breakdown of the power semiconductor device due to heating can thus be prevented.

Abstract: In a vertical field effect transistor including a source electrode and a gate on the front surface of a semiconductor substrate having one conductivity type and a drain electrode on the back surface of the substrate, the semiconductor device of the present invention has the structure wherein a connection region of one conductivity type positioned between two channel forming base regions of the opposite conductivity type is formed by a semiconductor layer having a higher impurity concentration than the drain region of the one conductivity type, and the surface portion of the connection region which is connected to the channel has a lower impurity concentration than the connection region.

Abstract: A V-MOS FET has a semiconductor body of one conductivity type, a plurality of base regions of the other conductivity type formed in a surface portion of the semiconductor body in a form of matrix having rows and columns, a plurality of source regions of the one conductivity type formed in the base regions, a plurality of auxiliary regions of the other conductivity type formed in the surface portion of said semiconductor body at crossing points of the rows and columns of the base region matrix, a mesh-shape gate electrode formed on region between the source regions to cover the auxiliary regions, a source electrode contacting at least the source regions and a drain electrode contacting a back surface of the semiconductor body.

Abstract: Herein disclosed is a vertical power MOSFET having a current sensing MOSFET, in which the base region of the current sensing MOSFET is electrically connected with the base region of the vertical MOSFET whereas the current leading-out electrode of the current sensing MOSFET is connected with only the source region of the current sensing MOSFET.