A cascode transistor circuit comprising: a drain output terminal; a source output terminal; a depletion-mode switch comprising a normally-on control terminal and a normally-on conduction channel; a normally-off switch comprising a normally-off control terminal and a normally-off conduction channel, wherein the normally-off control terminal is configured to receive a normally-off control signal for controlling the normally-off switch, and wherein the normally-off conduction channel is connected in series with the normally-on conduction channel between the drain output terminal and the source output terminal; a controller comprising a controller output terminal configured to provide a normally-on control signal for the normally-on control terminal of the depletion-mode switch to control the depletion-mode switch, wherein the normally-on control signal is independent of the normally-off control signal; a negative voltage source configured to provide a negative voltage to the normally-on control terminal of the depletion-mode switch; a feedback capacitance between the drain output terminal and a control node in a circuit path between the controller output terminal and the normally-on control terminal of the depletion-mode switch, characterized in that the negative voltage source comprises a bootstrap circuit connected between the controller output terminal and the normally-on control terminal of the depletion-mode switch, and the bootstrap circuit comprises a bootstrap capacitor and a bootstrap rectifier, wherein: the bootstrap capacitor is connected in series between the controller output terminal and the normally-on control terminal of the depletion-mode switch; and the bootstrap rectifier is connected in series between the normally-on control terminal of the depletion-mode switch and the source output terminal, wherein the feedback capacitance is connected between the drain output terminal and the controller output terminal. a drain output terminal; a source output terminal; a depletion-mode switch comprising a normally-on control terminal and a normally-on conduction channel; a normally-off switch comprising a normally-off control terminal and a normally-off conduction channel, wherein the normally-off control terminal is configured to receive a normally-off control signal for controlling the normally-off switch, and wherein the normally-off conduction channel is connected in series with the normally-on conduction channel between the drain output terminal and the source output terminal; a controller comprising a controller output terminal configured to provide a normally-on control signal for the normally-on control terminal of the depletion-mode switch to control the depletion-mode switch, wherein the normally-on control signal is independent of the normally-off control signal; a negative voltage source configured to provide a negative voltage to the normally-on control terminal of the depletion-mode switch; a feedback capacitance between the drain output terminal and a control node in a circuit path between the controller output terminal and the normally-on control terminal of the depletion-mode switch, the bootstrap capacitor is connected in series between the controller output terminal and the normally-on control terminal of the depletion-mode switch; and the bootstrap rectifier is connected in series between the normally-on control terminal of the depletion-mode switch and the source output terminal, wherein the feedback capacitance is connected between the drain output terminal and the controller output terminal.