An electrostatic discharge (ESD) protection circuit is provided. A first NMOS transistor is coupled to a power line. A second NMOS transistor is coupled between the first transistor and a ground. A detection unit provides a detection signal when an ESD event occurs at the power line. A trigger unit turns on the second NMOS transistor and the first NMOS transistor in sequence in response to the detection signal, such that a discharge path is formed from the power line to the ground via the first and second NMOS transistors.