We report on results that compare the planar confinement, diffusion, and surface segregation of Si δ‐doped in GaAs for growth by gas source molecular‐beam epitaxy and conventional molecular‐beam epitaxy. For gas source molecular‐beam epitaxy growth, Si diffusion versus inverse anneal temperature shows a unique two component Arrhenius form in which activation energies for diffusion differ by the fundamental GaAs band gap energy, 1.5 eV. Capacitance–voltage profiles of as‐grown δ‐doped Be and Si layers in GaAs produce record full width at half‐maximum, 1.9 and 2.4 nm, respectively, for the gas source molecular‐beam epitaxy case.