Systematic studies of as-grown MnAs films deposited by molecular-beam epitaxy on GaAs(001) and GaAs(113)A reveal that their magnetic properties and, in particular, their saturation magnetization are determined by the phase separation into stripes of ferromagnetic α-MnAs and paramagnetic β-MnAs. Using a specific saturation magnetization MS*, which refers to the actual volume of α-MnAs, the thickness dependence of MS* can be described in a universal way. It is due to the variation of the stripe structure and the changing of the intra- and interstripe magnetic interaction. Values well above ∼1100 emu/cm3, obtained for the optimum film thickness at room temperature, are considered as an intrinsic property of a nearly defect-free MnAs in the fully magnetized state. © 2004 American Institute of Physics.