| 摘要 |
PURPOSE:To improve withstanding voltage characteristic of a semiconductor device against a high voltage surge by forming a second conductivity type epitaxial layer on a first conductivity type substrate in such a manner that the thickness of a first epitaxial region is thinner than that of a second epitaxial region to facilitate the control of the thickness of an n-well and to reduce the ON resistance of the vertical MOSFET. CONSTITUTION:The thickness of a first epitaxial region 2a which serves as a region of a vertical MOSFET is formed in a predetermined thickness at a stepped portion of a P-type epitaxial layer 2, and the thickness of an n-well 4 which serves as a drain region is specified by the thickness of the region 2a. The thickness of the drain region is thinly formed to restrict the ON resistance to a low value at switching time, thereby obtaining a preferably operating characteristic. Since the region 2b is thickly formed at the layer 2 having high specific resistance, its withstanding voltage characteristic is held high. A surge of high voltage generated when a load current is interrupted is applied to a drain electrode 13: this surge is bypassed through a Zener diode having a predetermined current capacity to a source, thereby preventing a vertical MOSFET from damaging.
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