The onset of plastic relaxation via misfit dislocation (MD) formation in InxGa1-xN layers grown by metal-organic chemical vapor deposition on the (11 (2) over bar2) semipolar plane of GaN substrates is investigated using high-resolution X-ray diffraction, transmission electron microscopy and cathodoluminescence. The results of critical thickness calculations for MD formation as a function of InxGa1-xN alloy composition x are compared with experimental observations. MD generation is observed initially as a result of slip on the (0001) slip plane, and subsequently as a result of additional slip on inclined [1 (1) over bar 00} type m-planes, which eventually leads to an increase in threading dislocation density. (C) 2013 Elsevier B.V. All rights reserved.