A heatsink for a power device comprises an upper conductive plate providing a first surface; a lower conductive plate providing a second surface; a middle conductive plate provided between the upper and lower plates, the middle plate having a hollow portion and a solid portion, the hollow portion defining an area to receive coolant, wherein the power device is provided on the first or second surface, so that heat generated by the power device can be transferred to the coolant. The heatsink further comprises an input port coupled to the hollow portion of the middle plate to provide the coolant into the hollow portion; and an output port coupled to the hollow portion of the middle plate to remove the coolant from the hollow portion.