The effectiveness of the ZrB 2(0001) buffer layer for the metallorganic chemical vapor deposition (MOCVD) growth of Al xGa 1-xN on Si(111) substrates was demonstrated. It was observed that no unintentional Si doping occurs in the Al 0.2Ga 0.8N film even at the MOCVD growth temperature of 1050°C. It was shown that the intensity and FWHM of the CL peak corresponding to band-edge emission of 3.87 eV were comparable to those from a high-quality undoped Al 0.2Ga 0.8N commercial sample grown on sapphire. In-plane lattice constant of ZrB 2(0001), a=3.169 Å, has a small 0.6% mismatch with that of GaN(0001) where a=3.189 Å.