The growth mechanism for the formation of GaN nanorods using metalorganic chemical vapor deposition (MOCVD) selective area growth by pulsed source injection is proposed. The pulsed mode procedure and the kinetic model are discussed and experiments performed to support the model are described. The achievement of rod shape nanostructures grown by the pulsed mode can be attributed to two mechanisms: (1) the differences in the adsorption/desorption behavior of Ga adatoms on the c-plane (0001) and the boundary m-planes {11[overline]00}, and (2) the growth behavior of the semi-polar planes (especially the semi-polar {11[overline]00} plane).