The top silicon layers and the bonded Si/SiO2 interfaces in silicon-on-insulator (SOI) structures fabricated by (i) wafer bonding and hydrogen slicing, and (ii) by wafer bonding and chemical mechanical thinning (back-etch SOI, BESOI) were investigated and compared by charge deep-level transient spectroscopy. The hydrogen slicing was provided by hydrogen implantation into one of the bonded wafers and led to the high hydrogen concentration during SOI fabrication. Hydrogen presented in SOI during the fabrication process partially neutralizes the traps at the Si/thermal SiO2 interface, and completely neutralizes shallow acceptors and contamination with deep levels in the top silicon layer. (C) 2004 The Electrochemical Society.