A trench power MOSFET and a manufacturing method thereof are provided. The gate of the trench power MOSFET includes an upper doped region, a lower doped region and a middle region interposed therebetween. The upper has a conductive type reverse to that of the lower doped region, and the middle region is an intrinsic or lightly-doped region to form a PIN, P+/N− or N+/P− junction. As such, when the trench power MOSFET is in operation, a junction capacitance formed at the PIN, P+/N− or N+/P− junction is in series with the parasitic capacitance. Accordingly, the gate-to-drain effective capacitance may be reduced.