Using the conventional MOS planar process, miniature cantilever and doubly supported mechanical beams are fabricated from polycrystalline silicon. Poly‐Si micromechanical beams having thicknesses of 230 nm to 2.3 μm and separated by 550 nm to 3.5μm from the substrate are made in a wide range of lengths and widths. Two static mechanical properties are investigated: the dependences of maximum free‐standing length and beam deflection on the thickness of the beam. By annealing the poly‐Si prior to beam formation, both of these properties are improved. Nonuniform internal stress in the poly‐Si is apparently responsible for the beam deflection.