| 摘要 |
A semiconductor device is provided to prevent a parasitic bipolar transistor from turning on and to avoid latch-up by increasing the base density of a parasitic bipolar transistor. A semiconductor substrate(20) of one conductivity type is prepared. A first well(34) of an opposite conductivity type to that of the semiconductor substrate is formed in the semiconductor substrate. A second well(30) of one conductivity type is formed in the semiconductor substrate near the first well. A third well(28) is formed in the semiconductor substrate near the second well, having an opposite conductivity type to that of the second well and deeper than the second well. A fourth well(26) is formed in the semiconductor substrate between the second and third wells, having one conductivity type and deeper than the second well. The fourth well can be formed in the semiconductor substrate between the first and second wells. The first well can be deeper than the second well.
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