| 摘要 |
PURPOSE: To make a sustaining breakdown voltage higher in a high-breakdown voltage MOS transistor structure by constituting so that a substrate potential is less likely to become higher than the source potential. CONSTITUTION: While the concentrations and depths of the source- and drain-side offset diffusion layers 4d and 4s of a high-breakdown voltage MOS transistor are made equal to each other, the size of the source-side offset diffusion layer 4s is made larger than that of the drain-side offset diffusion layer 4d. In other words, dimensions Ld and Ls of the layers 4d and 4s are set as in the relation Ld < Ls. Therefore, the resistance value of the layer 4s becomes larger and the source voltage VS of the MOS transistor becomes higher. Consequently, a state, VW-(forward junction withstand voltage of silicon) <= VS (where, VW is the substrate voltage of the transistor), can be maintained easily and the sustaining breakdown voltage of the MOS transistor becomes high.
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