Epitaxial gallium arsenide films have been deposited on single crystalline GaAs substrates of {100} orientation and Si substrates of 3° off the {100} orientation by ArF excimer laser-induced metalorganic chemical vapor deposition. The important process parameters include the cleanliness of the substrate surface, substrate temperature, the composition, flow rate, and pressure of the reaction mixture, and the pulse energy and pulse rate of the laser. Particular attention was directed to the in-situ cleaning of the substrate surface prior to the deposition process. Homoepitaxial gallium arsenide films of good structural perfection have been deposited at 425°- 500 ° C and their single crystallinity has been confirmed by transmission electron microscopy. The carrier concentration decreases with increasing AsH3/(CH3)3 Ga molar ratio and with decreasing substrate temperature. Lower growth rate during the initial stage of deposition is necessary to obtain heteroepitaxial gallium arsenide films on Si with good structural perfection. The TEM examination of GaAs films of 0.15–0.2 µm thickness deposited on Si substrates at 500 °C has shown that stacking faults were present in the GaAs films; however, there is no apparent threading dislocations in the surface region of the thin GaAs film.