The local structure of epitaxially grownthin films of cobaltdeposited on GaAs(110) have been unequivocally determined to be the body‐centered phase, a metastable phase, by the use of conversion electron x‐ray absorption fine structure (conversion electron EXAFS). A detailed comparison of the data for a 350 Å Co film to similar measurements for polycrystalline bcc Fe, hcp Co, and fcc Cu concludes that the Co/GaAs thin films possess the metastable bcc structure with an extracted lattice constant of 2.82±0.01 Å. An observed reduction in the amplitude of the fine structure for the Co films is only partly due to distortion within these films, which is determined to be equivalent to an increase in a Debye–Waller factor of 0.0011 Å2. Replacing the GaAssurface with an epitaxially grown ZnSe surface, which maintains nearly the same lattice spacing, results in the formation of fcc and/or hcp Co. This first application of conversion electron EXAFS to single crystal epitaxialfilms shows it to be a most powerful procedure for establishing their crystal structure.