By using metalorganic vapor phase epitaxy, GaN layers are deposited on nominal Si(2 1 1) substrates that undergo different types of thermal treatment before the epitaxial growth. X-ray diffraction rocking curves and photoluminescence experimental results indicate that the crystal quality is improved significantly if the thermal treatment is composed of a high-temperature heating followed by a speedy cool-down process. It is observed that a high-temperature heat treatment alone on the substrates does not provide with measurable improvements in the GaN layers. In addition. atomic force microscopic images indicate that the easy glide system of Si( 1 1 1} plane can be also a source of residual stresses built up in the GaN film. Consequently, a suitable pre-thermal treatment for use on a silicon substrate is suggested to prevent the GaN film from suffering any extra stress arising from the substrate during the post-growth cooling process. (C) 2002 Elsevier Science B.V. All rights reserved.