Abstract: An isolation method for a semiconductor device, and comprises the steps of: sequentially forming a first silicon nitride film, an oxide film, and a second silicon nitride film on a substrate and forming an opening to define an isolation region between devices; forming a spacer at the edges of the opening and implanting impurities in the substrate; removing the exposed part of the first silicon nitride film, and then removing the spacer; growing a field oxide film, and sequentially removing the second silicon nitride film, the oxide film, and the first silicon nitride film. In a second embodiment, the first silicon nitride film and part of the substrate are removed, and then the spacer is removed during the process of removing the exposed part of the first silicon nitride film and the spacer. Accordingly, the depth to which the field oxide film is buried is controlled by the etching depth of the substrate, thereby increasing the effective isolation distance.