Dimethylethylamine alane (DMEAA) has been used to grow AlAs thin films by metalorganic molecular beam epitaxy. In situ reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) measurements indicate that high-quality AlAs films with atomically smooth surfaces can be epitaxially grown on GaAs(100) at relatively low temperatures (less than 550°C) with no detectable carbon or oxygen content by AES. Strong oscillations in the specular RHEED intensity indicates a layer-by-layer growth mode of AlAs using this new Al precursor. The growth rate, determined from the period of the intensity oscillations, is linearly dependent on the DMEAA partial pressure, but is independent of substrate temperature, at least in the range from 320 to 620°C. An enhancement of the Al adatom mobility over that obtained using an elemental Al source was observed.