GaN films were grown on patterned-Si(111) substrates by metal organic chemical vapor deposition (MOCVD). Arrays of rectangular stripes and squares, with a 3.5-mum height and different lateral dimensions were patterned and etched on Si substrates using inductively coupled plasma reactive ion etching. A low temperature 24-nm-thick AlN (grown at 720 degreesC) was used as the seed layer for growing GaN films of 0.3- to 2-mum thick. For ridges wider than 2 pm, crack-free flat-top GaN films were obtained with a surface roughness of similar to0.7 nm. Localized Raman spectroscopy was conducted to study the stress distribution in the GaN films on Si ridges and squares. Substantial stress relaxation was observed in GaN on patterned Si area. The crystalline microstructure of GaN films was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and atomic force microscopy. (C) 2004 Elsevier B.V. All rights reserved.