A broadband single pole four throw (SP4T) switch was designed, fabricated and fully evaluated in this paper. The switch is based on heterojunction AlGaAs/GaAs PIN diode, owing to its better performance in high frequency than homojunction device. Several vertical epitaxy structure PIN diodes were fabricated, measured and analyzed for switch branch designing. Based on serial-shunt diode unit, a monolithic microwave integrated circuit(MMIC) was fabricated which demonstrates superior broadband performance, measured results show that working from 50 MHz to 40 GHz, the 1.7 mm × 1.5 mm chip can achieve insertion loss in 1.2 dB, isolation more than 30 dB as well as excellent impedance match of all ports. Measured Input 1 dB compression point (IP 1dB ) is higher than 20 dBm. Fast switching speed is proved via an evaluated PCB, and the measured switching time is within 20 ns.