A mirror for an optical MEMS device has a plurality of segments supported on a substrate layer. Each segment includes a support post, a support layer, and a reflective layer formed over the support layer. The reflective layers of the plurality of segments form the reflective surface of the mirror. Due to the relatively small lateral dimensions of the segments, the mirror has a smaller thermal bow than prior art mirrors. The bow can be controlled, e.g., by appropriately choosing the number of segments and the layer thicknesses.