Horizontal MOSFET

A horizontal MOSFET comprising:

• a semiconductor substrate of a first conductivity type;
• a well region of a second conductivity type formed from a first surface of the semiconductor substrate;
• base regions of the first conductivity type formed on a first side in a surface layer of the well region;
• a drain region of the second conductivity type formed on a second side of the surface layer of the well region;
• source regions of the second conductivity type selectively formed in surface layers of the base regions;
• a gate electrode disposed through gate oxide film on a surface of a region extending from the source regions to an exposed surface area of the well region;
• a drain electrode contacting with the drain region;
• a source electrode contacting commonly with the source regions and the base regions;
• a substrate electrode contacting with an exposed area of the semiconductor substrate exposed on a side of the source electrode far from the drain electrode;
• and
• a current path of low resistance formed on a side of a second surface of the semiconductor substrate;
• wherein the current path comprises a layer with high impurity concentration formed in a surface layer of the second surface of the semiconductor substrate.

A horizontal MOSFET comprising:

• a semiconductor substrate of a first conductivity type;
• a well region of a second conductivity type formed from a first surface of the semiconductor substrate;
• base regions of the first conductivity type formed on a first side in a surface layer of the well region;
• a drain region of the second conductivity type formed on a second side of the surface layer of the well region;
• source regions of the second conductivity type selectively formed in surface layers of the base regions;
• a gate electrode disposed through gate oxide film on a surface of a region extending from the source regions to an exposed surface area of the well region;
• a drain electrode contacting with the drain region;
• a source electrode contacting commonly with the source regions and the base regions;
• a substrate electrode contacting with an exposed area of the semiconductor substrate exposed on a side of the source electrode far from the drain electrode;
• and
• a current path of low resistance formed on a side of a second surface of the semiconductor substrate;
• wherein the current path comprises an electrode layer which is in ohmic contact with the second surface of the semiconductor substrate;
• and
• wherein resistivity of the semiconductor substrate is 200 .OMEGA.cm or more, and a thickness thereof is thin enough to induce punch through by application of voltage corresponding to a reverse withstand voltage required for a PN junction between the drain region and the semiconductor substrate.

A horizontal MOSFET comprising:

• a semiconductor substrate of a first conductivity type;
• a well region of a second conductivity type formed from a first surface of the semiconductor substrate;
• base regions of the first conductivity type formed on a first side in a surface layer of the well region;
• a drain region of the second conductivity type formed on a second side of the surface layer of the well region;
• source regions of the second conductivity type selectively formed in surface layers of the base regions;
• a gate electrode disposed through gate oxide film on a surface of a region extending from the source regions to an exposed surface area of the well region;
• a drain electrode contacting with the drain region;
• a source electrode contacting commonly with the source regions and the base regions;
• a substrate electrode contacting with an exposed area of the semiconductor substrate exposed on a side of the source electrode far from the drain electrode;
• and
• a current path of low resistance formed on a side of a second surface of the semiconductor substrate;
• wherein the current path comprises an electrode layer which forms a Schottky junction with the second surface of the semiconductor substrate;
• and
• wherein resistivity of the semiconductor substrate is 200 .OMEGA.cm or more, and a thickness thereof is thin enough to induce punch through by application of voltage corresponding to a reverse withstand voltage required for a PN junction between the drain region and the semiconductor substrate.