Semiconductor device

A semiconductor device comprising:

• an n-type semiconductor substrate which includes an n-type impurity having a diffusion coefficient less than a diffusion coefficient of phosphorus;
• an n-type epitaxial layer which includes a high concentration region, an intermediate concentration region and a low concentration region formed in this order from the semiconductor substrate side and has a concentration gradient in which an n-type impurity concentration is decreased in a downward step-wise manner from the semiconductor substrate toward a crystal growth direction by the high concentration region, the intermediate concentration region and the low concentration region;
• and
• a trench structure which includes a trench formed in the low concentration region, an insulating layer formed on an inner wall of the trench and an embedded electrode which is embedded in the trench across the insulating layer;
• wherein the epitaxial layer has a high concentration transition region in which a concentration gradient inclines gently between the high concentration region and the intermediate concentration region, and a low concentration transition region in which a concentration gradient inclines gently between the intermediate concentration region and the low concentration region, and
• the trench structure penetrates through the low concentration transition region to reach the intermediate concentration region.