We explore the possibility of modifying the Schottky barrier height ill magnetic contacts to,n-GaAs, which may have implications for future spin injection applications. Epitaxial MnAs and MnSb are used as a test system. The substrate orientation has a strong impact, with rectifying characteristics for contacts on GaAs(0 0 1) and GaAs(1 1 1)B, but nearly Ohmic behaviour on GaAs(l I 1)A, The insertion of Si interface dipoles is not very effective in this material system,