Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising:

• a step of preparing a semiconductor layer, having a first impurity region of a first conductivity type formed at a surface layer portion;
• a step of setting an active region, in which a functional element is to be formed, in the semiconductor layer and introducing a second conductivity type impurity in a surface layer portion of the first impurity region so that the second conductivity type impurity is introduced along a peripheral edge of the active region to form a well region of the second conductivity type;
• a step of performing an oxidation treatment to form an oxide film, which exposes an inner side edge portion positioned at the active region side in the well region, and covers an outer side edge portion positioned at an opposite side with respect to the active region in the well region;
• and
• a step of introducing a second conductivity type impurity in the surface layer portion of the first impurity region in the active region to forma second impurity region of the second conductivity type that defines the active region.