The strain relaxation behavior of H-implanted Si0.8 Ge 0.2 /Si heterostructures containing a B-doped Si buffer layer was investigated. The annealed H-implanted SiGe/Si samples with a B-doped Si buffer layer exhibit an additional relaxation compared to those with an undoped Si buffer layer. At an annealing temperature of 900°C, relaxation ratios of the H-implanted samples with and without a B-doped Si buffer layer were determined to be 79 and 53%, respectively. The increased relaxation can be attributed to the formation of the larger H-filled bubbles along the interface on both sides of the B-doped Si region. Such an annealed H-implanted SiGe/B-doped Si heterostructure was further demonstrated to have a threading dislocation density of 4.7× 105 cm-2 with a root-mean-square roughness of only 0.48 nm. This work offers an effective approach to fabricate high quality strain-relaxed thin SiGe epilayers for high mobility device applications.