Since the parallel-circuit class-E power amplifier (PA) has the advantages of simple structure and high efficiency, it has been widely used in many applications. To solve the problem of narrow bandwidth and low efficiency of the parallel-circuit class-E PA, an improved technology for its output matching network was proposed in this paper. A hybrid π-type structure was used as the output matching network of the PA, which not only performed the conversion between the best impedance and the standard impedance within a wide working bandwidth, but also effectively suppressed the second harmonic component, in turn to improve the circuit’s efficiency. In order to verify the validity of the proposed theory, based on a 0.25 μm GaN HEMT process, a monolithic-integrated class-E power amplifier with simple structure, high efficiency and high power was designed in this paper. The post-layout simulation results showed that the output power was greater than 40 dBm, and the power-added efficiency was 51.8% to 63.1% in the 2.5～3.7 GHz operating frequency range. The size of layout was 2.4 mm×2.9 mm.