An optical MEM device is fabricated with a patterned device layer formed on a silicon wafer. Preferably, the patterned device layer is patterned with plurality of ribbons and/or access trenches. The central portion of the ribbon is released from the silicon wafer using a selective etch process, wherein a cavity is formed under the central portion of the ribbon, while opposing ribbon ends remain attached to the wafer. The selective etching process preferably utilizes an enchant comprising xenon difluoride. In accordance with further embodiments, the silicon wafer is doped, patterned or otherwise modified to enhance the selectivity of the etching process.