Abstract: A silicon substrate is selectively implanted with ions and heated in a oxidizing atmosphere. Thus an oxide film is formed on the substrate so that portions of the film formed on regions implanted with the ions is partly embedded in the substrate. Then the film is etched until the surface of the substrate is selectively exposed. An impurity is diffused into the exposed surface portions to form base regions in the substrate after which the process as above described is repeated to form windows for emitter diffusion and electrodes. Also silicon is epitaxially grown on a silicon substrate selectively provided with SiO.sub.2 films so that silicon in the form of a single crystal is grown on the exposed surface portions of the substrate while polycrystalline silicon grown on the SiO.sub.2 films. The above process is repeated to convert the polycrystalline silicon to silicon dioxide for separating the silicon regions on the exposed surface portions from one another.