We demonstrate piezoresistive transduction of mechanical motion from out-of-plane flexural micromechanical resonators made from stacked thin films. The resonators are fabricated from two highly doped polycrystalline silicon layers separated by an interlayer dielectric. We examine two interlayer materials: thermal silicon dioxide and stoichiometric silicon nitride. We show that via one-time dielectric breakdown, the film stack functions as a vertical piezoresistor effectively transducing the motion of the resonators. We obtain a gauge factor of ∼5, which is sufficient to detect the resonator motion. The simple film stack constitutes a vertically oriented piezoresistor that is readily integrated with micro- and nanoscale resonators. © 2009 American Institute of Physics.