A field effect device comprises a substrate of semiconductor on insulator type successively provided with a support substrate, an electrically insulating layer and a semiconductor material film. First and second source/drain electrodes are formed in the semiconductor material layer. A conduction channel is formed in the semiconductor material layer and separates the first and second source/drain electrodes. A counter-electrode is formed in the support substrate and faces the first and second source/drain electrodes and the conduction channel. The counter-electrode is formed by a doped area of the support substrate having a first doping impurity concentration which decreases from an interface between the electrically insulating layer and the support substrate.