Growth of ZnO films on GaAs(0 0 1) substrates is demonstrated using ZnS buffer layers by metalorganic molecular-beam epitaxy excited by electron-cyclotron resonance oxygen plasma. Bright near band-edge luminescence was observed at room temperature and the deep-level emission was found to make little contribution to the optical spectrum. The Stokes shift of the luminescence measured at 15 K with the photoluminescence excitation spectrum was almost absent. These distinguished features are the clear manifestations of the quite high optical quality of the ZnO films grown on GaAs substrates.