Abstract: A reduction in defects and lateral encroachment is obtained by .[.utilizing a high pressure oxidation in conjunction with.]. an oxidizable layer conformally deposited over an oxidation mask. .[.The.]. .Iadd.In one embodiment, the .Iaddend.use of high pressure oxidation provides for the formation of LOCOS oxide without the formation of defects. Any native oxide present on the substrate surface is removed by using a ramped temperature deposition process to form oxidizable layer and/or a high temperature anneal is performed to remove the native oxide at the substrate surface. In this embodiment, any oxide which can act as a pipe for oxygen diffusion is removed. Therefore, nominal or no lateral encroachment is exhibited..Iadd.Alternately, lateral encroachment can be controlled by intentionally growing an oxide layer on the substrate surface. .Iaddend.