Growth of GaN by metal-organic vapor phase epitaxy (MOVPE) on metallic zirconium diboride (ZrB 2 ) substrate was investigated. Cross-sectional transmission electron microscopy (TEM) showed that cubic ZrB x N 1-x is formed on the surface when ZrB 2 is exposed to ammonia-containing atmosphere, which protects the nucleation of GaN or AlN. We solved the problem by covering ZrB 2 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 ZrB 2 and the surface of Si-doped GaN. © 2003 Elsevier Science B.V. All rights reserved.