GaN is a widegap compound semiconductor, which is useful for optoelectronic devices operating in short wavelengths and at high-temperatures. The GaN films are usually grown on sapphire substrates at growth temperatures higher than 1000°C using MOCVD method [1-3]. For the growth of GaN films with excellent crystallinity and optical property, high V/III source gas ratio (NH 3/TMG>10,000) is required due to the decomposition-resistant property of nitrogen source-gas such as NH3. The reduction of the source gas consumption is strongly desired from the viewpoint of the resource savings. For the GaN growth at low V/III source gas ratios, excitation of NH3 is required. Among several methods, catalytic reaction of hot tungsten (W) wire surface with NH3 is very promising, because it produces high-density NHx radicals, in particular when the W fine wires with a mesh structure are used . Recently, heteroepitaxial growth of GaN films on Si substrates has been attempted, aiming at fabrication of various GaN electronic devices at a low cost [5-8]. A large lattice mismatch, however, also exists between GaN and Si, which is similar to the case between GaN and sapphire. In order to overcome this problem, insertion of a thin SiC buffer layer between them is useful . In our previous studies, GaN films were grown on SiC/Si(111) substrates by hot-mesh CVD using TMG and NH3. Photoluminescence spectra of GaN films grown on the SiC buffer layer, however, showed relatively strong yellow luminescence at RT . In this study, in order to further improve the crystallinity and the optical property, the insertion of AlN buffer layer between GaN and SiC layer was attempted.