Abstract: A process for doping a P-type substrate (50) by forming a layer (52) of silicon nitride, implanting N-type impurities through this layer (FIG. 7), forming a resist mask (54) which leaves at least one area of the substrate (FIG. 8) containing a part of the nitride layer exposed, implanting N-type impurities first with an insufficient energy and then with a sufficient energy to traverse the nitride layer, subjecting (FIG. 9) the substrate to a high temperature treatment in an oxidizing environment to form silicon dioxide pads (55) on the areas of the substrate not covered by the nitride layer, removing the nitride layer and performing an implantation of P-type impurities into the areas delimited by the pads. The process then continues with the removal of the pads and, in the conventional manner, with the formation of an epitaxial layer and selective doping of this to form P-type and N-type regions in it.