this paper mainly introduces a GaAs MMIC Wideband SP8T Switch. Firstly, every possible configuration is contrasted, the theories of basic GaAs switch configurations are mentioned. Secondly, the theories of basic GaAs switch configurations are mentioned. Subsequently, appropriate topology is selected for this SP8T switch. This switch has been realized by 0.5µm GaAs pHEMT process. this switch exhibits high performance: over DC~2.5GHz, insertion loss is lower than 1.27dB; The isolation is lower than 30dB; the ripple variation of insertion loss is less than ±0.1dB; input return loss is lower than 22dB; on state, output return loss is lower than 18dB; off state, over 0.2GHz-2.5GHz, output return loss is lower than 10dB; on and off time are less than 75ns. The layout of the switch with a chip size is 1.11 mm×1.51mm.