We report on the structural and magnetic characterization of Ni/Fe/MgO/Fe structures grown on GaAs(001) and InP(001). High-resolution transmission electron microscopy images confirm a good crystallographic order of the structures grown on GaAs(001). On the contrary, the structures grown on InP(001) do not show any long-range crystallographic order. For structures grown on GaAs(001), magneto optic Kerr effect analysis shows steps in the hysteresis loops corresponding to magnetization reversal processes that occur independently in both ferromagnetic (FM) films. No FM coupling between the bottom Fe and the top Ni/Fe films is detected. The coercivity of the bottom Fe film in the junction is increased in comparison to the Fe/GaAs(001) film of the same thickness most likely due to crystallographic defects. The defects are created in the top Ni/Fe bilayer and are spread over the whole single-crystalline structure. For structures grown on InP(001), a strong FM coupling is deduced from the hysteresis loops and is interpreted in terms of the orange-peel coupling.