Power amplifiers (PAs) are the most power-hungry component of the transmit chain in a base transceiver system (BTS). Efficiency of the PA thus plays a significant role in the overall efficiency of the transmitter. Today’s modern wireless communications networks need high data rates and low power consumption. Given that the bandwidth is limited, and frequency bands are expensive, therefore, spectral efficiency is of high importance. This is mainly achieved by varying the modulation techniques to accommodate higher data rates. Consequently, with the modern modulation techniques, there is a generation of high peak-to-average ratio power levels. This poses a challenge for the traditional PAs to have high efficiency not only at the peak power but also at back-off power levels. Although there are several techniques to enhance the efficiency at back-off such as envelope tracking, pulse modulation, Doherty PA (DPA) etc., however, there are certain limitations associated with these architectures especially bandwidth restrictions and the complex designs. In this work, an unconventional design architecture for Radio Frequency (RF) PAs is implemented which is based on reverse load modulation technique. The Reverse Modulated Dual-Branch (RMDB) PA uses a constant current-biased transistor in the carrier branch to realize optimal load modulation without using the impedance transformer at the output of the PA, unlike in conventional Doherty. A proof-of-concept monolithic microwave integrated circuit (MMIC) PA is designed using 0.25um Gallium Nitride (GaN) high-electron-mobility transistor (HEMT) and process from United Monolithic Semiconductor (UMS) for sub-6 gigahertz (GHz) wireless applications, centered at 3.6 GHz. This first ever fully integrated RMDB PA MMIC provides excellent gain flatness 10.5 dB (±0.5 dB) across 3.4 to 4.0 GHz bandwidth (BW) and delivers an output power of 39 decibel-milliwatt (dBm), (~ 8 watts), at saturation with drain efficiency of greater than 52% while maintaining greater than 38% at 10-dB back-off under continuous wave (CW) signal. This performance makes this design a promising candidate for future 5G and beyond applications.