Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of two main parameters on the growth of nanostructures were discussed. The phases formed were determined by the Gibbs free energy changes in the reactions. Various phases (CoSi, Co2Si) and morphologies, such as single-stem nanowires, three-dimensional (3D) nanowire networks, and aloelike nanostructures, have been synthesized. Very low turn-on field (1.42 V/μm) and good conductance obtained from field-emission and electrical property measurements, respectively, indicate that CoSi nanowires are potentially useful for electronic devices.