We report a novel fiber data distribution interface (FDDI) optical bypass switch using the surface-micromachining technology. In this design, all of the switches' components are made of polysilicon films and are monolithically patterned. The switch consists of four multimode optical fibers and a two-sided mirror sitting vertically on the top of a sliding plate which can be driven by an integrated micro-actuator. The gap between two in-line fibers are minimized to reduce insertion loss without using any lense. The total insertion loss of the switch has been measured to be 2.8 dB for the CROSS state and 3.1 dB for the BAR state with a LED source operates at 1.3 micrometers wavelegnth. The cross-talk between two states is measured to be 26.1 dB. The insertion loss and cross-talk can be improved further using different designs. Using this approach, the size, weight, and cost of current FDDI bypass switches can be dramatically reduced. Furthermore, the micromachined FDDI bypass switches are potentially integrable with the optical sources/detectors and controlling electronics.