We discuss progress and prospects for compound semiconductor MEMS and MOEMS, in particular GaAs-based devices. Various applications, such as optical switching, sensors and RF will be highlighted with a particular focus on distinguishing characteristics of compound semiconductors over silicon structures. We present our work on a 1x2-waveguide switch. Data on fabrication and performance of this GaAs/AlGaAs device will be presented. Devices are predicted to switch in less than 40 µsec. Switching voltages of 15 V and propagation losses of 0.8 dB/cm were measured.