Co thin films have been electrodeposited on n-type (001) GaAs. The structure and texture of the films were investigated using X-ray diffraction and transmission electron microscopy (TEM) while the magnetic properties were examined using a vibrating sample magnetometer. Structural evolution was found to be a function of the growth rate. A strong hexagonal close packed (hcp) Co (11(2) over bar 0)[0001]\\GaAs(001)[110] texture was observed for films grown at lower deposition rates. The magnetocrystalline anisotropy of the hcp Co lattice summed over the two in-plane variants resulted in fourfold anisotropic in-plane magnetization. Films grown at faster rates had decreased magnetic anisotropy due to increased structural dispersion. TEM analysis of several films (8.5-15 nm) revealed a thin body centered cubic (bcc) Co layer between the GaAs (001) and the hcp Co (11(2) over bar 0) overlayer. The bcc layer formed with a cube-on-cube relationship to the GaAs (001) substrate. The structural evolution was similar to that reported for films grown by other methods, such as molecular beam epitaxy, although the thicknesses at which the various magnetic transitions occurred differed significantly, most likely due to the different growth rates employed. (C) 2003 The Electrochemical Society. All rights reserved.