Power device with protection against undesirable self-activation

The MOS-type power device (1) has a drain terminal (4), a source terminal (3), and a gate terminal (2), and comprises a protection circuit (11) having a first conduction terminal connected to the gate terminal (2), via a diffused resistor (5), and a second conduction terminal connected to the source terminal (3). The protection circuit (11) has a resistance variable between a first value and a second value according to the operating condition of the power device (1). A first embodiment of the protection circuit (11) comprises an ON-OFF switch (12) made by means of a horizontal MOS transistor which has a control terminal connected to the drain terminal (4) of the power device (1). A second embodiment of the protection circuit (11) envisages the replacement of the ON-OFF switch (12) with a gradual-intervention switch (23) made by means of a P-channel JFET transistor having a control terminal connected to the gate terminal (2) of the power device (1).