The authors investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions. The tunneling magnetoresistance (TMR) effect was probed for different types of Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is increased and is observable at room temperature. If an epitaxial Fe/GaAs (001) interface is involved, the tunnel junction exhibits a bias dependent inversion of the TMR effect. This is a first experimental signature for band structure effects at an Fe/GaAs interface and is relevant for spin injection experiments. (c) 2006 American Institute of Physics.