Semiconductor device having lateral high breakdown voltage element

Claim 1

A semiconductor device having a semiconductor layer formed on a semiconductor substrate with a buried insulation layer interposed, with a high breakdown voltage element formed at said semiconductor layer, said high breakdown voltage element having first and second impurity regions of mutually opposite conductivity types formed on said semiconductor layer, said semiconductor device comprising: a wide band gap layer positioned at least in a region which is to have highest electric field strength in said semiconductor layer when breakdown voltage is applied to said high breakdown voltage element, and formed of a material having a band gap wider than that of said semiconductor layer; a conductive layer for a field plate formed in a floating state on the region of said semiconductor layer which is sandwiched between said first and second impurity regions with an insulation layer interposed, and capable of storing capacitance between itself and a first electrode electrically connected to said first impurity region as well as between itself and a second electrode electrically connected to said second impurity region; and a drift region positioned in said semiconductor layer between said first and second impurity regions and having same conductivity type as said first impurity region and a lower impurity concentration than that of said first impurity region; wherein said wide band gap layer has impurity of same conductivity type as said drift region and impurity concentration at least twice and at most ten times that of said drift region.