SiGe-free strained-Si-on-insulator (sSOI) is a promising structure for near-future CMOS circuits because it has benefits of both strained Si and SOI and it is free from problems relating to SiGe buffer layers. In this study, the strain state and thermal stability of sSOI substrates fabricated by the wafer bonding technique was investigated in detail by Raman spectroscopy and X-ray diffraction (XRD) reciprocal space mapping (RSM)