Process of making a semiconductor device using a silicon-on-insulator substrate

A method of manufacturing a semiconductor device, comprising the steps of:

• forming a first semiconductor layer containing an impurity on a semiconductor substrate at least the surface of the semiconductor substrate being made of an insulating material;
• selectively introducing an impurity into a surface region of said first semiconductor layer to form an impurity region of a first conductivity type in said surface region of the first semiconductor layer so as to leave the first semiconductor layer between said impurity region and said semiconductor substrate, said impurity region having an impurity concentration higher than the impurity concentration of said first semiconductor layer;
• forming a second semiconductor layer of the first conductivity type on said first semiconductor layer and on said impurity region;
• forming a dielectric isolating region in said first and second semiconductor layers to divide the first and second semiconductor layers into a first element region and a second element region, each of said element regions including a respective portion of said first and of said second semiconductor layers;
• and
• forming a bipolar transistor in said first element region of said first and second semiconductor layers which is isolated by said dielectric isolating region from said second element region, said first element region including said impurity region, wherein said impurity region is bounded laterally by said dielectric isolating region.