We have investigated the annealing temperature dependence of structural and electrical properties in heavily arsenic implanted GaAs which has a similar amount of excess arsenic to low temperature GaAs (LT‐GaAs). The fundamental properties of this material are quite similar to those of LT‐GaAs. High resolution x‐ray diffraction measurements have revealed that it has an increased lattice constant, which is reduced to the value of bulk GaAs by annealing between 300 and 400 °C. Electrical conduction in this material is dominated by hopping between deep states, which is also reduced by annealing above 350 °C. In samples annealed at temperatures ranging from 600 to 850 °C, the dominant electron trap isEL2; it has been confirmed by resistivity measurements withn‐i‐nstructures that the Fermi level is pinned byEL2. In samples annealed below 500 °C, the dominant electron trap is notEL2 but theU‐band, although electron paramagnetic resonance measurements show the existence of a large concentration of the ionized arsenic antisite defect (AsGa+). This supports the notion that theU‐band is formed by AsGadefects with slightly modified carrier emission properties compared withEL2. ©1995 American Institute of Physics.