A GaN semiconductor power switching device (Qmain) comprising an integrated ESD 1protection circuit is disclosed, which is compatible with driving Qmain with a positive gate-to-source voltage Vgs for turn-on and a negative Vgs for turn-off, during normal operation. The ESD protection circuit is connected between a gate input of Qmain and a source of Qmain, and comprises a clamp transistor Q1, a positive trigger circuit and a negative trigger circuit, for turning on the gate of the clamp transistor Q1 responsive to an ESD event at the gate input of Qmain. The positive and negative trigger circuits each comprise a plurality of diode elements in series, having threshold voltages which are configured so that each of the positive trigger voltage and the negative trigger voltage can be adjusted. The ESD circuit topology requires smaller integrated resistors and can be implemented with reduced layout area compared to conventional integrated ESD circuits.