This thesis demonstrates the feasibility of using a GaN monolithic reconfigurable matching network to provide variable load impedance matching coverage for microwave power amplifiers operating in the X-band (8-12 GHz). The National Research Council's GaN500 (0.5 micron) HFET process, fabricated at the Canadian Photonics Fabrication Center (CPFC), is employed throughout this work. An initial investigation of various switch topologies is first conducted, showing the advantages and limitations of using single and multi-transistor switch realizations for the development of a multi-stage
programmable impedance tuner (PIT). Then, the design, optimization, fabrication and testing of a single stage of the proposed PIT structure are presented. The results show an extensive range of impedance coverage on the Smith Chart can be achieved, although this range is limited by losses. Finally, the co-integration of the resulting programmable tuners within a GaN power amplifier circuit is simulated, and its performance is studied.