The magnitude of potential fluctuations due to remote ionized dopants is calculated for selectively doped heterostructures using unscreened and screened Coulomb potentials. Potential fluctuations are found to be minimized (corresponding to maximum carrier mobility) if the dopant distribution is &dgr;‐function‐like. Our experimental study of electron mobilities in selectively doped heterostructures grown by molecular beam epitaxy reveals that carrier mobility indeed increases as the thickness of the doped layer is reduced, in agreement with the calculation. A peak electron mobility of 5.5×106cm2/V s is obtained at low temperatures in a selectively &dgr;‐doped heterostructure.