SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide a semiconductor device capable of increasing its withstanding voltage regarding the semiconductor device with a buried oxide film between a supporting layer and an element forming layer. SOLUTION: A conductive plate 26 is brought to a floating potential in a DC, and a trench plate 24 is formed between a source electrode 28 and the buried oxide film 21, thus connecting the conductive plate 26 on the source electrode 28 side through the trench plate 24. Consequently, since the electrostatic capacity of the buried oxide film 21 to the source electrode 28 is reduced, the same effect as the electrostatic capacity is reduced by thickening the buried oxide film 21 can be obtained substantially. The conductive plate 26 can also be stabilized electrically because the trench plate 24 takes a GND potential by a connection to a ground for the external circuit of the source electrode 28. Accordingly, the breakdown strength of a high withstanding voltage transistor 20 can be increased. COPYRIGHT: (C)2006,JPO&NCIPI