Epitaxial lateral overgrowth (ELO) of GaN by metalorganic vapor phase epitaxy was carried out on Si substrates using new ELO-mask patterns. The groove or SiO2 mask pattern employed was a stripe in combination with a larger period grid (100mum x 100mum): the former is for the ELO of the GaN to reduce the threading dislocation (TD) density and the latter is for limiting the area of growth and to suppress the formation of cracks in the grown GaN. Crack-free GaN layers with a reduced TD density, ere successfully obtained for both types of Si substrate. i.e. the grooved Si substrate and the SiO2-masked Si substrate. The properties of GaN layers grown on these Si substrates are compared. (C) 2002 Published by Elsevier Science B.V.