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The development of a high power RF SP4T MMIC switch using AlGaN/GaN HFETs on Si substrate is reported for applications up to 2 GHz. The off-state capacitance(Coff) of a single-gate GaN based HFET is 250 fF and the on-state resistance (Ron) is 4.1 Omega at a gate length of 0.7 mum and a width of 1 mm. The MMIC SP4T switch with a size of 1.2 x 1.6 mm2 is implemented for system applications of three transmit paths and a receiver, of which each was configured with a series-shunt self-biased configuration. The switch has achieved an insertion loss of -0.95 dB with power handling of P(-0.1dB)=45 dBm at 1 GHz at the transmitter paths and an optimized isolation of better than 28 dB at the receiver path of up to 2.5 GHz. In addition, a high voltage switch driver using the GaN power HFET technology was designed with an input control voltage of 0/2.3 V to provide an output voltage of 0/28 V. This development provides a baseline design for our first generation MMIC switches in GaN technology.