In this paper, a two-stage trigger (TST) scheme is proposed to implement a low-capacitance and zero-ohm input resistance electrostatic-discharge (ESD) protection device for nanometer technologies. This scheme includes two different kinds of trigger devices. The diode string is the first trigger device, which provides the substrate current to trigger the output transistor on. As the output transistor is turned on, the source begins to inject the electrons. Thus, some of the electrons are collected to the anode of the silicon-controller rectifier (SCR) for driving it into the latch-up state. With the additional trigger device, the dimension of the main trigger device can be reduced to minimize its capacitance. Moreover, the output transistor can connect to the pad directly without any resistor since the diode string can be turned on before the output transistor is turned on.