Approximately 100 Angstrom thick, mirror-like, ordered tungsten layers were fabricated on (100) GaAs with chemical vapor deposition, using a W(CO)(6) precursor. Native oxides on GaAs were reduced with AsH3 pretreatment in a chemical vapor deposition chamber of tungsten. Secondary ion mass spectrometry and Rutherford backscattering spectroscopy analyses indicate tungsten-GaAs mixed layer not thicker than 20 Angstrom. The chemical vapor deposited tungsten was applied to fabrication of state of the art, low resistance contacts to GaAs layers grown with molecular layer epitaxy. Optimization of GaAs doping, pretreatment, and tungsten chemical vapor deposition conditions were necessary to obtain low contact resistance. Contact resistance, measured with the transmission line method, was 3 X 10(-7) Omega cm(2) to Te doped n-type GaAs and below 2 X 10(-8) Omega cm(2) to C doped p-type GaAs. Electrically active donor/acceptor concentrations in GaAs layers grown by molecular layer epitaxy were about one order of magnitude lower than expected from literature trend lines for these contact resistance.