The present invention provides a high-side driver circuit including a power transistor, the first transistor, the second transistor, the second capacitor, the second diode, a start-up circuit. The start-up circuit is coupled between a resistor and the second capacitor to complete a gate driving circuit. And, the aforementioned resistor can either be the gate resistance of the power transistor or an external resistor. The design of start-up circuit enables the functionality of the bootstrap capacitor of being charged to a designate voltage level. Thus, the depletion-mode transistor can be controlled to turn on/off without a floating voltage source or a negative voltage source.