A power-on reset circuit includes a clamping signal generator and a determining device. The clamping signal generator is adapted to receive a trigger signal, and generates a clamping signal with reference to the trigger signal. The clamping signal generator includes an output unit for generating the clamping signal according to a feedback signal, and a feedback unit for generating the feedback signal according to first and second intermediate signals. The first intermediate signal is generated with reference to the clamping signal. The second intermediate signal is generated according to the trigger signal. The determining device is adapted to receive the trigger signal, is coupled to the clamping signal generator for receiving the clamping signal therefrom, and is operable to generate a reset signal according to the trigger signal and the clamping signal.