We show that while polystyrene ( PS) thin films are structurally unstable on oxidized silicon wafers, the addition of as little as a few weight percent tetramethylbisphenol A polycarbonate (TMPC) has a stabilizing effect on the topographical structure of the films. The stabilization is evident from the existence of a threshold TMPC concentration, phi(t), and a threshold thickness, h(t), beyond which films do not dewet. The concentration threshold occurs for phi(TMPC) <= 0.10. An examination of the effective interface potential, which accounts for short- and long-range intermolecular interactions, indicates that this dewetting inhibition is metastable.