We have grown film structures by molecular beam epitaxy which include GaAs buffer layers grown at low substrate temperatures (250°C). The film structures have been examined using transmission electron microscopy. The layers grown at normal temperatures (600°C) were free of defects or clusters. In contrast, the layer which was grown at low substrate temperatures contained precipitates which have been identified as hexagonal arsenic. The density of the arsenic precipitates is found to be very sensitive to the substrate temperature during growth.