A method for forming a component in a portion of a semiconductor substrate on insulator delimited by a lateral wall separated by an insulating layer from a peripheral region internal to the portion and heavily doped of a same first conductivity type as the substrate. A conductive plate is formed at the same time as the wall, on a layer of protection of the substrate surface, in electric contact with the peripheral region, the plate extending above said peripheral region towards the inside of the portion with respect to the wall, beyond the location above the limit between the peripheral region and the substrate.