Strained Si channel layers grown on relaxed SiGe layers have become attractive for the application to high-speed Si-based devices. Several methods have been developed in order to realize high-quality strain-relaxed SiGe buffer layers which induce the strain in the channel. In this work, we have used an ultra-thin Ge interlayer (with a thickness in the range of 0.5-5.0 nm) formed at the SiGe/Si(0 0 1) substrate interface to obtain thin strain-relaxed SiGe buffer layers. By using this method, we have not only controlled the residual strain of SiGe buffer layers but also realized thin strain-relaxed SiGe buffer layers with smooth surfaces. Moreover, we have confirmed the changes of dislocation structures as the thickness of Ge interlayer increased. This structural change of dislocations leads to the effective strain-relaxation along the direction parallel to the interface. (C) 2003 Elsevier B.V. All rights reserved.