To provide a semiconductor device for preventing deterioration of element isolation breakdown voltage, and for improving the yield of a fragmented and highly integrated semiconductor device, and a method for manufacturing the semiconductor device.

The surface of a substrate 41 is oxidized at a temperature which is 1,050°C or higher, or oxidized at an oxidizing rate which is 7.5 mm/ minute or higher so that an oxide film 43 which is 1,500 nm or larger in thickness can be formed. When this oxide film 43 is removed, the surface density of pits existing on the surface of the substrate 41 is becomes not more than the facial density of pits existing on the surface of the substrate 41 before the oxidizing treatment, and the depth of pits existing on the surface of the substrate 41 becomes 50 nm or smaller.