Selectively doped GexSi1-x/Si strained layer heterostructures have been grown in a single quantum well configuration on 〈001〉‐Si substrate using molecular beam epitaxy. The modulation doping effect has been observed in p‐type structures only; although both n‐ and p‐type double heterostructures were grown. We have investigated the effects of: (i) alloy layer thickness (well width), (ii) doping setback, and (iii) cladding layer dopant concentration, on the hole mobilities. At present, optimum structures show peak hole mobilities in excess of 3300 cm2V-1s-1 at 4.2 K, sheet charge densities of 3.0–14×1011 cm-2, and hole effective mass m h =0.32±0.03 m0. It is found that the low temperature (T∼10 K) hole mobility, in structure having x=0.2 is relatively insensitive to alloy layer (well) thickness in the range 100 Å≲Lw≲Lc; where Lc is the critical thickness marking the transition from strained layer to relaxed, misfit accommodated, alloy growth. For Lw≫Lc, misfit dislocation scattering dramatically decreases μh at T≲100 K; whereas for Lw≲100 Å the hole mobility is uniformly lowered over the entire range of measurement temperatures. Doping setback and cladding layer dopant concentration affect the mobility via changes in sheet charge density, in a manner consistent with theoretical expectations. The absence of the modulation doping effect in n‐type heterostructure is taken as an indication that ΔEv≫ΔEc.