The segregation of B fromSi1−xGexquantum wells grown using molecular beam epitaxy on Si(100) and Si(110) was investigated using secondary ion mass spectrometry. When a 3 nm B doping slab(n=1019/cm3)was placed in the center of a 6 nmSi1−xGexquantum well, the B profiles had two distinct exponential decay lengths,&Dgr;SiGe, the Ge-controlled B decay length and&Dgr;Si, the B decay length normally measured in Si.&Dgr;SiGewas the same for Si(100) and Si(110) and independent of Ge concentration in the well for0.1⩽x⩽0.5.As the Ge concentration was increased in the well, the location of the transition point, from&Dgr;SiGeto&Dgr;Si,which was always found far outside of the SiGe quantum well, increased in distance from the center of the well.