Epitaxial growth of transition-metal Cr-doped cubic-phase GaN (GaCrN) layers on GaAs (0 0 1) substrates by plasma-assisted molecular-beam epitaxy and the observation of ferromagnetism above room temperature are reported for the first time. Influence of V/III ratio and Cr-cell temperature on the physical properties of the grown layers is studied extensively. X-ray diffraction studies and transmission electron microscopy observations confirm the predominantly cubic-nature of GaN and GaCrN for the epitaxial layers grown under Ga-rich condition. Cr dopant atoms exhibit surfactant nature and improve the crystalline quality and also enhance the growth of cubic-phase of GaN and GaCrN. Strong and broad blue-luminescent band (centered at 2.85 eV) is induced by the Cr doping in GaN. The saturation magnetization of the grown layers initially increases with Cr concentration and then decreases for further increase of Cr concentration. (C) 2007 Elsevier B.V. All rights reserved.