We are developing single-crystalline silicon micromirror arrays (MMA) fro future generation infrared multiobject spectroscopy (IR MOS). The micromirrors are 100 mu m x 200 mu m in size and can be tilted by electrostatic actuation yielding a tilt-angle of 20 degrees. Arrays of 5x5 micromirrors were gold-coated and tested at below 100K. The coated and uncoated micromirrors are optically flat (peak-to-valley deformation < lambda/20 for lambda > 1 mu m) at room temperature and in cryogenic environment. Successful actuation has been done at room temperature and at temperatures below 100K. Large arrays of 200x100 micromirrors are being fabricated and an actuation scheme for extremely large arrays has been developed.