This invention discloses a trigger circuit for an electrostatic discharge (ESD) protection device, the ESD protection device being turned on during an ESD event and being turned off during a normal operation, the trigger circuit comprises a voltage sensing circuit coupled to a bonding pad, the voltage sensing circuit being configured to produce a first predetermined voltage during a ESD event, and to produce a second predetermined voltage complimentary to the first predetermined voltage during a normal operation, and a voltage converting circuit having a positive feedback circuit and coupled between the voltage sensing circuit and the ESD protection device for converting the first predetermined voltage to a third predetermined voltage for turning on the ESD protection device, and for converting the second predetermined voltage to a fourth predetermined voltage for turning off the ESD protection device.