In the growth of InGaN/GaN multi-quantum well (MQW) heterostructures by metal organic chemical vapor deposition, V-defects attached to threading dislocations have been observed and investigated. Energy-dispersive X-ray analysis and conventional transmission electron microscopy studies were carried out in order to determine the In composition and investigate the behavior of the dislocations. The V-defects are limited by {1011} lattice planes, they are attached to threading dislocations and may start at the third quantum well. The associated dislocation runs up into the overgrown GaN layer. Some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. (c) 2004 Elsevier B.V. All rights reserved.