Epitaxial films of CuInSe2 are grown on GaAs (001) wafers using metalorganic vapor phase epitaxy in a horizontal reactor for fundamental optical and electrical transport investigations. In this article we present the growth parameters and structural properties of the epitaxial CuInSe2 thin film. The growth parameters are optimized. in particular growth temperature and gas floats. The optimum growth temperature for CuInSe2 is 500 degreesC with a growth rate of approximately 90 nm/h. At 450degreesC CuInSe2 exhibits some polycrystallinity within the otherwise single crystalline lacer. Attempts to grow CuInSe2 on GaAs at 570degreesC lead to Ga interdiffusion in the CuInSe2 layer. Layers with different [Cu]/[In] ratios are examined by photoluminescence to identify intrinsic defect levels. (C) 2002 Elsevier Science B.V. All rights reserved.