A function module with built-in heat dissipation device. The function module includes a first circuit board, a second circuit board, a first height-compensation heat spreader, a second height-compensation heat spreader, and a heat dissipation fin. The first circuit board has a first surface, a first and second device. The second circuit board has a second surface facing the first surface, a third device, and a fourth device. The first height-compensation heat spreader has a first face, contacting the first and second devices simultaneously, and a third face, opposite to the first face. The second height-compensation heat spreader has a second face, contacting the third and fourth devices simultaneously, and a fourth face, opposite to the second face. The heat dissipation fin is disposed between the first circuit board and the second circuit board.