| 摘要 |
PROBLEM TO BE SOLVED: To provide a technology which can improve the avalanche breakdown strength of a field-effect transistor. SOLUTION: This MOS-FET has a body region 32 and a buried region 22 which is formed under the body region 32 and constitutes a first P-N junction 85 with the body region 32. If a high voltage is applied to the MOS-FET 1, the first P-N junction 85 is broken down by an avalanche breakdown, and a current is made to flow through the first P-N junction 85. However, since the first P-N junction 85 is formed on the bottom surface of the body region 32 and has a large area, even if a large current flows through the first P-N junction, the current is distributed uniformly over the whole junction and is hardly concentrated, so that a device breakdown cause by concentrating of current is hardly produced.
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