US Patent 7851277 Semiconductor device and method of manufacturing same

An object is to reduce the adverse influence which a portion of a gate insulating layer where the thickness has decreased, that is, a step portion, has on semiconductor element characteristics so that the reliability of the semiconductor element is improved. A semiconductor layer is formed over an insulating surface; a side surface of the semiconductor layer is oxidized using wet oxidation to form a first insulating layer; a second insulating layer is formed over the semiconductor layer and the first insulating layer; and a gate electrode is formed over the semiconductor layer and the first insulating layer with the second insulating layer interposed therebetween.