Abstract: A method of manufacturing semiconductor devices having one or more insulated gate field effect transistors in which a sunken oxide layer is obtained by local oxidation. In those cases in which above a doped zone a thin insulating layer is necessary, for example because said layer forms the dielectric of a capacitor, the invention provides a simplification of the manufacture in that at area in question a thicker sunken oxide layer is first provided which is removed fully or partly in a later stage so as to be able to obtain the desired thinner layer.