Abstract: A switching device of a load comprises: two switching terminals; a depletion-mode high-voltage transistor and an enhancement-mode low-voltage transistor arranged in series between the two switching terminals and defining a midpoint; a control circuit generating a control signal of the gate of the low-voltage transistor in order to selectively place the device in an on state or in an off state; a power-supply circuit comprising an input connected to the midpoint and an output for supplying a power voltage to the control circuit. The power-supply circuit comprises a reservoir capacitance connected to a normally-on switch for charging the reservoir capacitance and supplying the power voltage to the control circuit when the switching device is connected to the load.