  We investigated spin dependent transport through Fe/GaAs/Fe tunnel junctions.
The tunneling magnetoresistance effect (TMR) was probed for different types of
Fe/GaAs interfaces. For interfaces cleaned by hydrogen plasma the TMR effect is
increased and 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 a Fe/GaAs interface and relevant for spin injection experiments.
