This paper presents a novel type of lateral series microwave switch on a silicon-on-insulator (SOI) substrate with a coplanar waveguide (CPW) configuration. It is built with a cantilever beam at the side of the gap of the microwave t-line and laterally driven by electrostatic force. The mechanical structures are made of single-crystal-silicon and fabricated by deep reactive ion etch (DRIE) technology. Evaporated aluminum serves as contact material. The fabrication process only needs one mask. The measured result shows up to 26.5 GHz the isolation of the switch is over 18 dB. The threshold voltage is about 12 volts. © 2003 IEEE.