| 摘要 |
PROBLEM TO BE SOLVED: To prevent reduction of an element breakdown voltage. SOLUTION: A silicon active layer 2 is formed on an oxide film 2 buried in a silicon substrate 1. The silicon active layer 3 is formed therein with a trench which reaches the buried oxide film 2, the trench is formed with a side wall oxide film 6, and the remaining part of the trench is filled with polycrystalline silicon. When the silicon active layer 3 has a thickness tSI and a distance from the trench to a p-n junction 8 is set to be Liso, a relation of Liso>(√2.tSI)/2 is satisfied.
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