The propagation properties of inversion domains (IDs) in InGaN/GaN multiple quantum well (MQW) structures grown by metalorganic chemical vapor deposition have been investigated by transmission electron microscopy (TEM). The majority of the IDs, originating from the sapphire and/or buffer layer, propagate through the MQWs, with normal wurtzite structure retaining their original structural features. Some of IDs could induce V-shaped pits in the MQW structures proposing a new formation mechanism for the so-called V-shaped defects. Detailed measurements show that a few IDs are found to be stopped in abnormal MQW regions. where In droplets appear due to phase separation, We presented direct evidence of pure In-phase droplets by means of high-resolution TEM. The above results provide new information on the structural defects in InGaN/GaN-based materials. (C) 2002 Elsevier Science B.V. All rights reserved.