We have made a comparative study of the oxygen out-diffusion process during heat treatment of SOI wafers and SiC-SOI hybrid substrates. SOI materials with three different thicknesses (2, 20 and 410 nm) of buried oxide (BOX) were used in the investigation High-resolution cross-sectional transmission electron microscopy (HRXTEM) together with laser interferometry was used to determine the remaining thickness of the BOX-layer after heat treatment. After complete removal of the BOX-layer of SOI wafers, the St/Si interface appears to be sharp and defect-free. Similar results were obtained for SiC-SOI hybrid substrates after removal of the entire buried oxide layer. For all combinations investigated oxide removal was accompanied by a thickness reduction and roughening of the silicon surface layer as verified by atomic force microscopy (AFM). (C) 2009 Elsevier Ltd All rights reserved.