This paper reports a simple and systematic experiment to distinguish various types of defects in bonded wafer pairs with the dynamic blade insertion (DBI) method and real-time observation. In addition, a type of defect was observed in bonded wafer pairs after they were heated to 1273 K and unevenly cooled. It exhibits a fairly large size with coarse Newton-ring contours in IR observation. During DBI examination, these defects exhibit quite a different behavior from other types of defects (void, dust particle, etc.) with the significant intention of resisting the movement of the approaching blade. However, this defect demonstrates a very strong bonding strength in tensile testing. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3442794] All rights reserved.