Carbon‐doped GaAs films have been grown by solid‐source molecular beam epitaxy using a graphite filament. The films were doped from 1×1015cm−3to 5×1019cm−3and the resulting mobilities are equivalent to beryllium‐doped films. A slight dependence of As4/Ga flux ratio on carbon doping was observed. The use of either As2or As4did not significantly affect the carbon doping concentrations. Lattice contractions were observed for films doped heavily with carbon or beryllium. For a given doping concentration the contraction is more significant for carbon doping which is consistent with the smaller tetrahedral covalent radius of carbon compared to beryllium. Good agreement between observed and calculated lattice contractions with carbon doping is obtained. Annealing studies on a film doped with carbon at 5×1019cm−3indicate that the electrical properties and lattice contraction are quite stable.