Plastic deformation in (001) SiG-on-insulator (SGOI) substrates during Ge condensation has been studied with emphasis on planar defect formation. Multiple slip deformation is found to be a dominant mode of the plastic deformation during the condensation toward Ge-rich SGOI substrates and to form stacking faults associated with Lomer-Cottrell dislocations for Ge composition higher than approximately 0.4. The multiple slip bands are also found to be a homogeneous slip line consisting of successive slips of lattice plane and/or deformation twinning of {111} bands. The double cross-slip mechanism is responsible not only for the slip deformation but also for deformation twinning during the condensation. (C) 2008 Published by Elsevier B.V.