Patent ID: 7476947

Claim:
A semiconductor device comprising: a high breakdown voltage MOSFET that includes a source region of a second conductivity type and a drain region of the second conductivity type formed apart from each other in a well region of a first conductivity type; a channel region formed between the source region and the drain region; a gate insulation film formed on the channel region; a LOCOS oxide film having a greater film thickness than the gate insulation film and formed adjacent to the gate insulation film; and a gate electrode formed across the gate insulation film and the LOCOS oxide film; wherein the drain region includes a first drain region formed apart from the gate electrode, a second drain region covering the first drain region and formed in a region including at least a region under the LOCOS oxide film, and a third drain region covered with the second drain region at least at a lower part thereof and formed in a region including at least the region under the LOCOS oxide film; said second drain region is aligned with a boundary between the LOCOS oxide film and the gate insulation film; said first drain region is located in said second drain region; said third drain region is not in surface contact with the channel region; and the first drain region has a higher concentration of impurities of the second conductivity type than the third drain region, and the third drain region has a higher concentration of impurities of the second conductivity type than the second drain region.