Growth of GaN by metal-organic vapor phase epitaxy (MOVPE) on metallic zirconium diboride (ZrB2) substrate was investigated. Cross-sectional transmission electron microscopy (TEM) showed that cubic ZrBxN1-x is formed on the surface when ZrB2 is exposed to ammonia-containing atmosphere, which protects the nucleation of GaN or AlN. We solved the problem by covering ZrB2 surface with very thin AlN or GaN at low temperature, thereby achieving high-quality GaN growth with a dislocation density less than 10(8) cm(-2). Direct conduction was achieved through the back of ZrB2 and the surface of Si-doped GaN. (C) 2003 Elsevier Science B.V. All rights reserved.