Systematic site-specific comparisons of the densities of threading dislocations (TDs) and associated V-defects in six-period InxGa1-xN/GaN multi-quantum wells (MQWs) with In mole fractions of x=0.1 and 0.2 have been conducted using several electron microscopy techniques including electron channeling contrast imaging. The MQWs were grown on GaN epitaxial films deposited on either (0001) GaN substrates or on (0001)AlN/6H-SiC heterostructures. The densities of TDs and V-defects in the surfaces of the homoepitaxial GaN films and the In0.1Ga0.9N/GaN MQWs were both 5.5 x 10(6) cm(-2). By contrast, the V-defect densities in the In0.2Ga0.N-8/GaN MQWs exceeded by two and three times the densities of TDs measured in the surfaces of the underlying GaN films grown on GaN and AlN/SiC substrates, respectively. Similar observations of V-defects not associated with threading dislocations have been previously reported to occur in InGaN MQWs grown on GaN template films on sapphire substrates and having either an initially high In mole fraction or grown at the end of a series of MQWs with an increasing In mole fraction. From a synthesis of the results of this previous work using GaN/sapphire substrates with the present results for bulk GaN substrates, it is hypothesized that increases in stress generated by the larger mismatches in lattice parameters between the GaN film and the In0.2Ga0.8N/GaN MQWs and the additional stresses generated between the GaN barriers and the wells within these MQWs generated new TDs within the MQWs, which then acted as nucleation centers for new V-defects. (C) 2013 Elsevier B.V. All rights reserved.