Abstract: Circuitry is provided which increases the efficiency of electrostatic discharge (ESD) power supply clamping circuitry to sink larger currents during an ESD event on a power supply node. Voltage clamp circuits capable of providing ESD protection to a supply node are described. The voltage clamp circuits include a discharge transistor which is controlled by a control circuit during an ESD event. The control circuit operates in response to a voltage provided on the protected supply node. One embodiment provides a P-channel MOS transistor and a control circuit which drives the gate of the transistor. Another embodiment provides an N-channel MOS transistor and a control circuit which drives the gate of the transistor.