The annealing behavior of low temperature (LT)-GaAs layers was investigated using transmission electron microscopy, x-ray rocking curves, and H+ ion channeling. These data were compared to the Hall-effect and conductivity data obtained earlier on the same samples. An expansion of the lattice parameter above those observed for as-grown LT-GaAs layers was observed for the layers annealed at 300 and 350 degrees C. No precipitation was observed in transmission electron micrographs for these annealing temperatures. Based on ion-channeling results, the As atoms (split interstitials) appear to be in the same position as found for the as-grown layers. A special arrangement of As split interstitials or out-annealing of gallium vacancies would be consistent with a decrease of the dominant acceptor in these layers and an increase in the lattice parameter. For annealing above 400 degrees C, the lattice parameter decreased and in fact was found to achieve the substrate value at annealing temperatures of 500 degrees C and above. The decrease in the lattice parameter above 400 degrees C is related to the decrease of excess As antisite defects and As split interstitials in the formation of As precipitates.