The influence of 300 keV electron irradiation on the behaviour of post-implantation defects in GaAs at room temperature has been investigated. The effect opposite to defect annealing, i.e. the increase of post-implantation damage level has been observed. The n-GaAs wafers of <100> orientation were implanted with 150 keV As⁺ ions at RT. The implantation doses of 1 and 2x10¹³ ions cm^-2 at a constant flux of 0.1 mA cm^-2 were employed to create disorder level below the amorphization threshold. Then the samples were irradiated with a scanned beam of 300 keV electrons to a total dose of 1x10¹⁷ cm^-2. The electron beam intensity of 1 mA cm^-2 was used to maintain the sample at constant temperature not excceding 320 K. The depth damage distributions of post-implantation defects before and after electron irradiation have been measured by using RBS and channeling spectroscopy of 2 MeV ⁴H⁺ ions. The results show a distinct increase of a damage level after electron irradiation which amounts to about 100% of the initial damage created for both ion implantation doses. Tentative explanation of this effect is based on the reported earlier observations that ionization changes the charge state of defects. As a consequence, rearrangement of defects takes place, giving rise to their out-diffusion from the clusters created by ion implantation, increasing in this way a total level of damage.