We report the growth and photoluminescence (300 and 4.2 K) characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on sapphire substrates using various growth conditions. The (0001) Al2O3c‐plane substrates are oriented exactly (0001) or misoriented either 2° towards theaplane (112¯0), 5° towards themplane (101¯0), or 9° toward themplane. A comparison of the 300 and 4.2 K optical characteristics of the samples grown on the different substrates indicates that a higher photoluminescence intensity is measured for the films on misoriented substrates. ©1996 American Institute of Physics.