Abstract: A method of manufacturing semiconductor devices of the type wherein regions of oxide such as silicon oxide recessed or inset in a silicon substrate are formed by oxidation of the silicon with the use of a masking layer protecting locally against the oxidation. In order to prevent the formation of a projecting oxide beak under the masking layer a nitride oxidation mask is applied directly to the substrate which has been previously ion-implanted to a controlled depth and then annealed to generate a dense dislocation network array on the substrate surface to prevent mechanical stress defects which normally would occur when a nitride mask is applied directly to a substrate.