High breakdown voltage semiconductor device having a resurf layer

A semiconductor device, comprising:

• a semiconductor substrate having a first conductivity type and having an upper surface on which a recessed part is formed;
• an electrode layer formed in a surface of said semiconductor substrate so as to be adjacent to said recessed part and having a second conductivity type;
• a reduced surface field layer formed in said semiconductor substrate so as to be in contact with a bottom surface of said recessed part and said electrode layer and containing impurities of said second conductivity type lower in concentration than said electrode layer;
• an insulating oxide film formed on the upper surface of said semiconductor substrate so as to entirely fill said recessed part;
• and
• a field plate electrode formed directly on a top surface of said insulating oxide film above said recessed part, wherein
• a depth of the recessed part from the bottom surface of the recessed part to the upper surface of the semiconductor substrate filled entirely by the insulating oxide film is greater than a thickness of the insulating oxide film outside of the recessed part,
• a film thickness of said insulating oxide film in said recessed part is 1.0 μm or more, and a thickness of a gap extending from the top surface of said semiconductor substrate outside of the recessed part to a bottom surface of the field plate electrode formed directly on the top surface of said insulating oxide film, the thickness of the gap corresponding to the thickness of the insulating oxide film outside of the recessed part, is less than 1.0 μm, and
• a ratio between the depth and the thickness is substantially 2:1.