GaN films were grown by metal organic chemical vapor deposition on (1 1 1)Si substrates, using AlN as a buffer layer. The influence of the AIN buffer layer growth temperature and growth duration on the morphology and preferred orientation of GaN films was studied. Drastic enhancement of epitaxial registration was observed with increasing buffer growth temperature. A sharp transition in the growth mode occurred at 760 degrees C. For that temperature, an optimal buffer layer growth duration was found. The use of March parameter as a figure of merit in X-ray diffraction testing of textured GaN films is proposed.