The spatial resolution of the capacitance‐voltage profiling technique on semiconductors with one‐dimensional quantum confinement is shown to be given by the spatial extent of the wave function. The Debye length limitation does not apply. Capacitance‐voltage profiles on &dgr;‐doped GaAs of density 4–4.5×1012cm−2exhibit widths of 20 and 48 A˚ forp‐ andn‐type impurities, respectively. The profiles agree with the theoretical resolution function and with Be and Si profiles measured by secondary‐ion mass spectroscopy. It is further shown that the saturation of the free‐carrier density of highly Si &dgr;‐doped GaAs grown by molecular beam epitaxy is due to inactive Si impurities