| 摘要 |
PROBLEM TO BE SOLVED: To provide a semiconductor device for which the rise of a process cost is reduced, element formation is facilitated, an almost uniform electric field is formed in the thickness direction of a semiconductor substrate, and the trade-off (effective ON resistance) of a withstand voltage and ON resistance is improved. SOLUTION: A DMOS transistor in which a main current flows between the first main surface and second main surface of a silicon substrate is formed. The DMOS transistor is provided with a p-type diffusion region 3 formed on the first main surface, an n<+> diffusion region 5 formed on the first main surface within the p-type diffusion region 3, and a gate electrode 6 facing the p-type diffusion region 3 held between the n<+> diffusion region 5 and an n<-> layer 1 through a gate insulation layer 12. A dielectric layer 11 is formed inside the silicon substrate so as to be adjacent to the n<-> layer 1, and the dielectric layer 11 is composed of a material having a dielectric constant higher than the one of silicon.
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