A new photoluminescence (PL) technique has been developed and applied to nondestructively image defects at the bonded interface in thick silicon-on-silicon (Si-Si) fusion-bonded wafers. Transmission electron microscopy and energy dispersive X-ray spectroscopy were used to identify the nature of the defects observed by the PL method. The detection and mapping of threading dislocations, slip dislocations, and oxide agglomerates was possible with high resolution, through silicon layer thicknesses of 40 mm. The technique was used to compare the interface quality for three different hydrophilic and hydrophobic prebond cleans. The results were correlated with secondary ion mass spectroscopy and spreading resistance measurements across the interface, showing that the electrical properties and generated defect type are strongly related to the structure and chemical composition of the interface at the join. (C) 2003 The Electrochemical Society.