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 300°C to 900°C. 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 500°C, with significant barrier degradation at 600°C. At 700°C 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 800°C Co2AS formed, and at 900°C only CoGa3 and Co2As phases remained in contact with GaAs.