ZnO layers have been deposited by electron beam (EB) evaporation and laser ablation molecular beam epitaxy (MBE) as buffer layers to grow GaN by metal organic vapor phase epitaxy (MOVPE). The photoluminescence spectrum of the ZnO layer deposited by an EB evaporator shows an emission peaks of 367 nm. GaN was grown on ZnO/Si, Si and sapphire substrates under the same growth condition employing low-temperature-grown AIN buffers to prevent the dissociation of ZnO during the high GaN growth. The GaN on ZnO/Si shows sharp photoluminescence spectra at room temperature and 10 K. These results indicate a potential use of ZnO/Si substrates for GaN based blue-UV optical devices such as vertical-cavity surface-emitting lasers (VCSELs).