Semiconductor device and method for manufacturing the same

A semiconductor device including a plurality of units having identical structures, each of which comprising:

• a drain electrode;
• a drift layer that includes a low concentration layer on the drain electrode and a reference concentration layer on the low concentration layer,
• the reference concentration layer including an impurity of a first conductive type at a first concentration, and
• the low concentration layer including an impurity of the first conductive type at a concentration lower than the first concentration;
• a gate electrode on the reference concentration layer;
• a pair of source regions that are provided on an upper surface of the reference concentration layer and in the vicinity of both ends of the gate electrode, and include an impurity of the first conductive type at a concentration higher than the first concentration;
• a pair of base regions that surround outer surfaces of the source regions and include an impurity of a second conductive type at a second concentration;
• a source electrode electrically connected to the source regions and the base regions;
• and a pair of depletion-layer extension regions that are provided under the base regions in the reference concentration layer and include an impurity of the second conductive type at a concentration lower than the second concentration, wherein
• first boundaries between the depletion-layer extension regions and the low concentration layer are positioned lower than a second boundary between the reference concentration layer and the low concentration layer.