GaAs wafers with the Si doped epitaxial layers were bombarded by double energy of oxygen ions with 250 keV and 100 keV of 10¹² cm^-2 ¸ 5 x 10¹³ cm^-2 doses followed by 500^oC annealing process. Temperature dependence of the layer resistivity was evaluated in the temperature range 30¸423 K for the above structures to estimate the conduction mechanism in the material. Variable range hopping conductivity dominated at temperatures up to 300 K for high ion doses (5 x 10¹³ cm^-2) and up to 250 K for lower doses (10¹³ cm^-2). At higher temperatures, the resistivity data plotted indicated a transition from hopping to conduction through the extended states.