Abstract: A method of manufacturing a semiconductor device is provided in which a masking layer is formed on a part of a surface of a monocrystalline semiconductor body and the semiconductor body is then subjected at the side of the surface to an epitaxial treatment from a gaseous phase, and an epitaxial layer is deposited of which a portion on the uncovered part of the surface is monocrystalline and a portion on the masking layer is polycrystalline. This method is characterized in that, prior to the epitaxial treatment, an amorphous or polycrystalline layer is deposited both on the masking layer and on the uncovered part of the surface at a temperature which is lower than that at which the epitaxial layer is deposited. In this layer the layer portion on the uncovered surface part changes into the monocrystalline state by a thermal treatment preceding the deposition of the epitaxial layer.