Photoreflectance has been used to study the Fermi level of annealed low-temperature GaAs in sample structures composed of low-temperature GaAs on top of Si-delta-doped GaAs. The diffusion of As precipitates across the interface between low-temperature GaAs and normal GaAs is observed by cross-sectional imaging via transmission electron microscopy. We have calculated the Fermi-level pinning in low-temperature GaAs by including the Si-delta-doped carrier concentration correction due to the accumulation of As precipitates. The Fermi level is found to decrease from 0.7 to 0.5 eV below the conduction band when the annealing temperature is increased from 600 degrees C to 900 degrees C. This may be explained with the buried Schottky barrier model. (C) 1998 American Institute of Physics.