Copper metallized AlGaAs/InGaAs psedomophic high-electron-mobility transistor (PHEMT) single-pole-double-throw (SPDT) switches utilizing platinum (Pt, 70 nm) as the diffusion barrier is reported for the first time. In comparison with the Au metallized switches, the Cu metallized SPDT switches exhibited comparable performance with insertion loss of less than 0.5 dB, isolation larger than 35 dB and the input power for one dB compression (input P 1 db ) of 27 dBm at 2.5 GHz. These switches were annealed at 250° for 20 h for thermal stability test and showed no degradation of the dc characteristics after the annealing. Also, after 144 h of high temperature storage life (HTSL) environment test, these switches still remained excellent and reliable radio frequency (RF) characteristics. It is successfully demonstrated for the first time that the copper metallization using Pt as the diffusion barrier could be applied to the GaAs monolithic microwave integrated circuits switch fabrication with good RF performance and reliability.