thin films have been grown on Si(100) substrates at low temperatures of 500-850 degrees C by metal-organic molecular beam epitaxy (MOMBE) using the solid precursor magnesium acetylacetonate. Oxygen plasma is required to achieve deposition. The composition of the films was determined by Auger electron spectroscopy (AES). The as-deposited films are phase-pure, stoichiometric, crystalline MgO with a [100] texture. Carbon contamination of the film resulting from precursor decomposition was not observed within detection limits. The deposition rate depended superlinearly on the plasma source power.