Co-Ni-Cu/Cu multilayers were electrodeposited directly onto n-doped GaAs substrates with two different crystal orientations, (001) and (111), without the use of any seed layer. X-ray diffraction and transmission electron microscopy showed that epitaxial growth occurred on GaAs(001), with either the {001} or {211} planes parallel to the substrate, but not on GaAs(111). On this substrate, the multilayers grow preferentially with the {111} planes parallel to the substrate, but the crystallites have no preferred orientation in-plane. The presence of superlattice satellite peaks in the X-ray data for the multilayers grown on GaAs(001) and their absence for those frown on GaAs(111) indicated that the latter had a less perfect layer structure, Multilayers grown on both substrates exhibited giant magnetoresistance (GMR). For small Cu layer thicknesses, t(Cu) < 20 Angstrom, the GMR was suppressed for multilayers grown on both substrate orientations. For t(Cu) between similar to 20 and similar to 30 Angstrom, the GMR was much greater for the multilayers electrodeposited on GaAs(001) than for those on GaAs(111), while for larger layer thicknesses, the GMR for both substrate orientations was similar. This behavior can be explained qualitatively by the presence of different numbers of defects producing different degrees of ferromagnetic coupling in the two sets of multilayers.