The growth of a GaS film on both GaAs (100)-(2X4) and -(4X2) surfaces using a directional beam of [(Bu-t)GaS](4) has been studied in ultrahigh vacuum with high-resolution electron energy loss spectroscopy, Auger electron spectroscopy, low-energy electron diffraction (LEED), and temperature programmed desorption. At a surface temperature of 650 K, the growth of a GaS film with no measurable carbon contamination was observed. Upon adsorption of a monolayer of GaS, the surface forms a (2X1) reconstruction. Upon further adsorption, as a multilayer of GaS film was deposited, a (1X1) LEED pattern was observed. The resulting film had a S to Ga ratio identical to that grown via metal organic chemical vapor deposition and exhibited a vibrational mode at 350 cm(-1) which is attributed to the cubic phase GaS phonon mode. Upon annealing a surface, which was exposed to [(Bu-t)GaS](4) at a surface temperature of 100 K, desorption of isobutylene and hydrogen was observed at a temperature of 650 K. In agreement with this, hydrocarbon vibrational mode intensities corresponding to the t-butyl ligands began to rapidly decrease at 600 K and disappeared completely by 650 K. This suggests that beta-hydride elimination is the dominant mechanism for t-butyl ligand detachment at the growth temperature of similar to 650 K.