Cu epitaxial films were grown on H-terminated Si(110) and Si(111) substrates by magnetron sputtering. The epitaxial orientation of the Cu films and microstructural characteristics were studied by X-ray diffraction, including the conventional theta-2 theta mode and pole figures, and transmission electron microscopy (TEM). The results of pole figure analysis show an epitaxial orientation relationship of Cu(111)//Si(110) with Cu[(1) over bar 10]//Si[001] and Cu[1 (1) over bar 0]//Si[001] which are twin-related. The TEM observations of the cross-sectional samples reveal that the Cu film contains a layered structure due to growth twins. The reason for twin formation is discussed.