Abstract: In order to provide rapid turn-off of a transistor (or thyristor) having its emitter (or cathode) at a floating potential, on drive is removed from the base of the transistor T1 and almost simultaneously a switch SW1 is closed. This causes a proportion of the current which flows through a capacitor C on turn-off of the transistor T1 to flow through a resistor R1 by way of the base of the transistor T1, thus providing a reverse base current which rapidly turns-off the transistor T1. In a practical implementation of this circuit the switching device is a transistor T.sub.off and the circuit employs a self-timing approach in which removal of an "on" control signal from the gate of a field-effect transistor T7 automatically actuates the reverse current drive.