High-quality SiGe films with a buffer layer containing Ge quantum dots have been grown by ultra-high vacuum chemical vapor deposition. For Ge dots/Si bilayers up to 10 periods, threading dislocation density and the residual strain in the SiGe uniform epilayers were found to reduce drastically with the increasing period. The Si0.8Ge0.2 film grown on a 10-period Ge dots/Si bilayers was demonstrated to have a threading dislocation density of 2.0 × 105 cm- 2 with a residual strain of only 11%. Strained-Si n-channel metal-oxide-semiconductor transistors with various buffer layers were fabricated and examined. Effective electron mobility for the strained-Si device with the multiple Ge quantum dots buffer layer was found to be 90% higher than that of Si control device. The scheme for the formation of the relaxed SiGe film serving as a virtual substrate shall be applicable to high-speed strained-Si devices.