This thesis presents two different types of high-power gallium nitride (GaN) phase shifters designed for X-band (8–12 GHz) but offering good performance over a much wider band. The first type of phase shifter is a novel design having 22.5° phase shift, which promises wide bandwidth (in this case limited by the SPDT switch also designed), but achieves decent insertion loss (5 dB), good return loss (better than 11 dB) and very low phase variation (1°) across X-band. The components for a 45° differential phase shift using the same structure were also fabricated and verified with measurements. The second type of phase shifter is a 22.5° switched-filter phase shifter which has much wider bandwidth than is typically found with this configuration, while maintaining low insertion loss (<2 dB), good return loss (>11.15 dB) and an amplitude imbalance of less than 1.03 dB across X-band. The 1 dB compression point was higher than the laboratory equipment was able to measure (>38 dBm) and the phase shifter monolithic microwave integrated circuit (MMIC) exhibited an input-referred third-order intercept point (IIP3) higher than 46 dBm. A K-band phase shifter was also designed to test the limits of the technology. The high-power phase shifters have been fabricated in a 0.5 μm GaN HEMT process and were designed using an accurate, customized switch HEMT model. Suspended inductors offering improved quality factor and increased self-resonance frequency were also used in the design of some of the phase shifters.