In this paper, we report the fabrication of ferromagnetic semiconductor on GaN substrates by high-dose Cr ion implantation. Both magnetic and optical properties for Cr+-implanted GaN were studied by photoluminescence and superconducting quantum interference device. The results of photoluminescence reveal that the implanted chromium incorporates substitutionally on Ga site and forms deep acceptor level in GaN. The materials show ferromagnetic-like order up to 300 K as indicated by temperature-dependent magnetization measurement. The M vs. T curve also implies the presence of different components to the magnetization in Cr+-implanted GaN. (c) 2004 Elsevier B.V. All rights reserved.