The effect of thermal annealing on the electrical conductivities of arsenic‐ion‐implanted GaAs has been investigated by deep level transient spectroscopy and temperature‐dependent conductance measurements. For the annealed films of arsenic‐ion‐implanted GaAs a band of deep‐level defects with the activation energy of around 0.55 eV below the conduction band is found. The dense concentration of traps is able to reduce the carrier concentration from 3×1018to 2×1017cm−3. The cross section of the deep level is calculated to be 1.5×10−14cm2. The carrier‐transport mechanisms of both as‐implanted GaAs and postannealed GaAs are dominantly shown to be a separate hopping and active‐type conduction. ©1996 American Institute of Physics.