Crystal growth of GaAs by switched laser metalorganic vapor phase epitaxy (SL MOVPE) is reported. This growth technique is achieved by combining laser MOVPE and atomic layer epitaxy. The growth process in SL MOVPE can be explained by a model which assumes that trimethylgallium adsorbed on the crystal surface is decomposed in a photocatalytic reaction and that the decomposition rate depends on the surface species present on the substrate.