Lateral thin-film SOI devices with graded top oxide and graded drift region

A lateral thin-film Silicon-On-Insulator (SOI) device comprising a semiconductor substrate, a thin buried oxide insulating layer on said substrate, and a lateral semiconductor device provided in a thin semiconductor film on said thin buried oxide, said thin semiconductor film comprising a first region of a first conductivity type, a second region of a second conductivity type opposite to that of the first and spaced apart from said first region by a lateral drift region of said second conductivity type, a top oxide insulating layer over said thin semiconductor film, and a conductive field plate on said top oxide insulating layer, characterized in that said top oxide insulating layer comprises a layer portion adjacent said first region which increases in thickness in a substantially continuous manner in a direction from said first region toward said second region over a distance of at least about a factor of five times greater than a maximum thickness of said thin semiconductor film, and said lateral drift region comprises a region portion adjacent said first region which decreases in thickness in said substantially continuous manner in a direction from said first region toward said second region over a like distance of at least about a factor of five times greater than a maximum thickness of said thin semiconductor film.