A power switch circuit is disclosed. The power switch circuit includes an input terminal, an output terminal, a power switch, a control circuit and a voltage holding circuit. The power switch is coupled between the input terminal and the output terminal. The power switch has a control terminal. The control circuit is coupled to the input terminal and the output terminal respectively. The control circuit compares a first voltage of the input terminal with a second voltage of the output terminal to generate a control signal. The voltage holding circuit is coupled to the control circuit and the control terminal. The voltage holding circuit provides a default voltage larger than 0 V to the control terminal according to the control signal.