Abstract: An X-band transmitter front-end monolithic microwave integrated circuit (MMIC) has been developed utilizing 0. 25μm gallium nitride HEMT technology. The MMIC contains an integrated single-pole double-throw (SPDT) switch and a power amplifier. The SPDT switch is symmetrically composed of two parallel HEMTs at each way. While the power amplifier is designed using 3-stage topology, reactance matching networks have been employed to improve the output power and efficiency. Across the frequency range of 8 ~12 GHz, the transmitter MMIC delivers an output power of 38. 6 ~ 40. 2 dBm with power added efficiency (PAE) of 29% ~34. 5%. The insertion loss of the switch is about 0. 8 dB, and the isolation is more than 45 dB. The chip size is 4 mm×2. 1 mm.