The synthesis of wurtzite gallium nitride (GaN) nanorods with triangular shape on c-Al2O3 substrates using a thermal chemical vapor deposition process was investigated. It was possible to control nanorod shape and growth mode of GaN nanorods by change of sample geometry in the chamber using a mixture of GaN powder and Ga metal with ammonia gas reaction. It was found that the GaN nanorods were grown via both vapor-liquid-solid and vapor-solid mode with change of sample placement in the chamber. The morphology of the GaN nanorods was observed by field-emission scanning electron microscopy in secondary electron and back-scattered electron mode. High-resolution transmission electron microscopy, and X-ray scattering measurements revealed the GaN nanorods to have a single-crystalline wurtzite structure. (C) 2008 Elsevier B.V. All rights reserved.