Vertical semiconductor device and method of manufacturing the same

A vertical semiconductor device comprising:

• a layered semiconductor structure including a semiconductor substrate of a first conductive type having a first impurity concentration, a first semiconductor layer of the first conductive type formed on the semiconductor substrate and having a second impurity concentration lower than the first impurity concentration, and a second semiconductor layer of the first conductive type formed on the first semiconductor layer and having a third impurity concentration lower than the second impurity concentration;
• a source region of the first conductive type formed in a surface region of said second semiconductor layer;
• at least one gate electrode extending from a front surface of said layered semiconductor structure through said second semiconductor layer to reach said first semiconductor layer;
• a gate oxide film located between said gate electrode and said first and second semiconductor layers;
• an insulating film formed on said gate electrode at said front surface of said layered semiconductor structure;
• a source electrode formed on said source region of the first conductive type;
• a drain electrode formed on said semiconductor substrate of the first conductive type at a rear surface of said layered semiconductor structure;
• and
• a region of a second conductive type formed in a portion of said surface region of said second semiconductor layer between two adjacent gate electrodes at a lower level with respect to the source region, such that the region of second conductive type is separated from the two adjacent gate electrodes by said second semiconductor layer, and wherein the source electrode is in contact with a surface of the region of second conductive type.