Ferromagnetic bcc-FexCo1-x(100) films have been successfully grown on GaAs(100) and ScyEr1-yAs(100) by molecular beam epitaxy. X-ray diffraction combined with reflection high energy electron diffraction and low energy electron diffraction patterns revealed the epitaxial orientation of bcc-FexCo1-x(100)< 010 >parallel to GaAs(100)< 010 > and bcc-FexCo1-x(100) < 010 >parallel to ScyEr1-yAs(100)< 010 >. Rutherford backscattering channeling minimum yields, chi(min)similar to 3%, suggest epitaxial films of high crystalline quality. Vibrating sample magnetometry measurements show in-plane uniaxial anisotropy and fourfold in-plane anisotropy for FexCo1-x grown on GaAs(100) and ScyEr1-yAs(100), respectively. The difference in magnetic anisotropy is interpreted as arising from the ScyEr1-yAs interlayer altering the surface symmetry from twofold symmetry for GaAs(100) to fourfold symmetry. Misoriented substrates were also used to increase the step density in the [011] direction, which induced an additional uniaxial anisotropy with a [011] easy axis and a [01 (1) over bar] hard axis. This step structure symmetry-induced magnetic anisotropy generated a split field similar to 50 Oe in the hard axis for bcc-FexCo1-x(100) grown on ScyEr1-yAs(100) surfaces.