An ESD device is provided for protecting a circuit from electrostatic discharge, and includes a planar diode having an anode and a cathode. The anode is electrically coupled to a signal path of the circuit, and the cathode is electrically coupled to a ground of the circuit. The ESD device is configured to be off during normal operation of the circuit and to turn on in response to an electrostatic discharge on the signal path. Two depletion regions in the device are separated by an isolation well. In response to the electrostatic discharge, the depletion regions modulate (e.g., widen and merge), providing a path for the discharge to the ground of the circuit.