A high voltage device includes a high voltage transistor and a protection device. The high voltage transistor has a first end and a second end, in which the first end is coupled to a voltage input/output terminal. The protection device is coupled between the second end of the high voltage transistor and a ground terminal, and has a parasitical equivalent circuit. When the voltage input/output terminal is charged based on positive ESD charges, the current corresponding to the positive ESD charges flows from the voltage input/output terminal through the high voltage transistor and the equivalent circuit in the protection device toward the ground terminal. A power management circuit is also disclosed herein.