We investigate modulation‐doped InxGa1−xAs/AlyGa1−yAs quantum wells grown by molecular beam epitaxy with respect to carrier mobility and its dependence on In content, In distribution, populations of electron subbands, and local positions of electron wave functions. We find that the room‐temperature electron mobilities are dominated by the In contents at the maxima of the electron wave functions rather than by the average In contents. At 77 K the mobilities are most strongly influenced by the distance between doping layers and the maxima of the electron wave functions. As a practical result of this study, we present a quantum well structure for high electron mobility transistors with a carrier mobility as high as 8100 cm2/V s at 295 K for an electron density of 2.5×1012cm−2. ©1996 American Institute of Physics.