The reduction of the dislocation density in relaxed SiGe/Si heterostructures using a low-temperature Si(LT-Si) buffer has been investigated. We have shown that a 0.1 &mgr;m LT-Si buffer reduces the threading dislocation density in mismatchedSi0.85Ge0.15/Siepitaxial layers as low as∼104 cm−2.Samples were grown by both gas-source molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition. ©1997 American Institute of Physics.