The authors have observed that for Inx Ga1-x N epitaxial layers grown on bulk GaN substrates exhibit slip on the basal plane, when in the presence of free surfaces that intercept the heterointerface and for indium compositions x0.07. This leads to almost complete relaxation of the local misfit strain by generation of radial-shape dislocation half loops. For x0.17, generation of straight misfit dislocations by glide on the secondary 〈11 2- 3〉 {11 2- 2} slip system is observed, in addition to the radial-shape half loops at surface pits. These two mechanisms act independently with no observed interaction between them, leading to the conclusion that slip on the basal plane occurs first during the growth process. The secondary slip system is activated later and involves a significantly higher critical stress energy. © 2006 American Institute of Physics.