GaN layers are grown by metalorganic chemical vapor deposition (MOCVD) on Si(1 1 1) substrates. X-ray diffraction (XRD) measurements and cross-section transmission electron microscopy (TEM) show a comparable crystalline quality of the samples to the quality of GaN/sapphire samples. Both the characteristic symmetric GaN(0 0 0 2) and the asymmetric GaN(10 - 15) X-ray reflections have full-widths at half-maximum of 600-700 arcsec. The dislocation density as estimated from TEM investigation is found to be of the order of 10(10) cm (-2). The initially deposited AlAs nucleation layer is transformed into AIN by supplying ammonia to the AlAs layer. This buffer layer can be completely etched off thus providing an easy way for substrate-layer separation after growth, an essential step for avoiding absorption of radiation emitted from nitride layers in the silicon substrate.