X-ray diffraction studies and current-voltage measurements have been performed on a (100) oriented single crystal thin film of CoxGa1-x (x = 0.42) grown epitaxially on n-GaAs, from 300C to 900C. At this composition, CoxGa1-x, which has a broad range of homogeneity and a variable lattice parameter, is lattice matched to GaAs better than 0.5%. A Schottky barrier height of 0.68eV and an ideality factor of 1.07 have been measured up to 500C, with significant barrier degradation at 600C. At 700C formation of the CoGa3 phase and a shift in CoxGa1-x stoichiometry to its bulk thermodynamically most stable composition of Co.45Ga.55 was observed with x-ray diffraction. At 800C Co2AS formed, and at 900C only CoGa3 and Co2As phases remained in contact with GaAs.