A power amplifier and a signal transmitting system using the power amplifier are disclosed. The power amplifier includes a circuit board, a power amplifier, and a structural component. The circuit board is fixed on the structural component. The power amplifier is fixed on the circuit board or the structural component. A grounding reference layer is set on the structural component. A pair of pins is set on the power amplifier. A pair of housing portions is set between the circuit board and the structural component. Overhead matching areas are set face to face with the housing portions on the circuit board respectively. Power amplification matching portions are set face to face with the reference layer on the matching areas respectively. The pins are electrically connected to the power amplification matching portions respectively.