A fully integrated GaN Doherty power amplifier (DPA) Monolithic Microwave Integrated Circuit (MMIC) plays a critical role in WLAN applications, which demonstrates high gain and efficiency. This work introduces a modified ∏-type output network to enhance the bandwidth. Furthermore, a pre-driver is used to enlarge the gain and decrease the amplitude to phase (AM/PM) variation. The designed DPA demonstrates a simulated saturation power of 37.2-37.6 dBm, a high gain of 20.3-22.8 dB, a saturation power added efficiency (PAE sat ) of 44.0-47.4 % and a 6-dB back-off power added efficiency (PAE bo ) of 31.8-41.7 %. Moreover, the AM/PM is less than 2 degree at the 1dB compression point of 34.8 dBm. The third-order Inter-Modulation Distortion (IMD3) and fifth-order Inter-Modulation Distortion (IMD5) are below -18 dBc and -30 dBc. This work is a promising candidate for the high-demanding WLAN applications.