An etching mask, comprising the delineation pattern of the gate electrode, of a source contact, a drain contact and a counter-electrode contact, is formed on a substrate of semi-conductor on insulator type. The substrate is covered by a layer of dielectric material and a gate material. The counter-electrode contact is located in the pattern of the gate electrode. The gate material is etched to define the gate electrode, the source contact and drain contacts and the counter-electrode contact. A part of the support substrate is released through the pattern of the counter-electrode contact area. An electrically conductive material is deposited on the free part of the support substrate to form the counter-electrode contact.