Abstract: A method of manufacturing a semiconductor device, in which a layer (12) comprising silica and an oxide of a dopant is provided on a surface (9) of a silicon semiconductor body (1). The semiconductor body is then subjected to a heat treatment at a temperature at which transport of the dopant takes place from its oxide to the seminconductor body. The heat treatment is carried out at a first stage in an atmosphere comprising an inert gas to which up to 25% by volume of oxygen is added, at a second stage in an atmosphere of practically dry oxygen and then at a third stage in an atmosphere comprising oxygen and hydrogen. Thus, a doped zone is formed in the semiconductor body, while the surface is covered with an insulating layer of high quality.