We investigated the electrical transport properties in Co 2FeAl0.5Si0.5 (CFAS)/GaAs junctions. From current density-voltage characteristics, the formation of a schottky tunnel barrier in the CFAS/GaAs interface was indicated. Moreover, junction resistance of 2× 10-9 Ω·m2 which is adequate for high magnetoresistance ratio attributable to high spin injection efficiency was obtained. Comparing the bias dependencies of conductance with samples, which CFAS ordering is lower, indicated that L21 ordered CFAS contributes to electrical transport. Finally, the spin injection signal was observed with 3-terminal Hanle measurement, and spin relaxation time was estimated to be 380 ps at 5 K.