This invention is generally concerned with semiconductor-on-insulator devices, particularly for high voltage applications. A lateral semiconductor-on-insulator device is described, comprising: a semiconductor substrate; an insulating layer on said semiconductor substrate; and a lateral semiconductor device on said insulator; said lateral semiconductor device having: a first region of a first conductivity type; a second region of a second conductivity type laterally spaced apart from said first region; and a drift region extending in a lateral direction between said first region and said second region; and wherein said drift region comprises at least one first zone and at least one second zone adjacent a said first zone, a said first zone having said second conductivity type, a said second zone being an insulating zone, a said first zone being tapered to narrow towards said first region.