HfO2/Al2O3 nanolaminated stacks prepared by atomic layer deposition have been investigated in terms of their charge storage characteristics for possible application in charge trapping memories. It is shown that the memory window, electron and hole trapping and leakage currents depend strongly on Al2O3 thickness and post-deposition oxygen annealing. Depending on the Al2O3 thickness, post-deposition annealing in O2 creates different electrically active defects (oxide charge and traps) in the stacks. O2 annealing increases electron trapping, thus giving rise to a larger memory window and enhanced charge storage characteristics, i.e. 65% of charge is retained after ten years and the memory window decreases by 6% after 2.5 × 104 program/erase cycles.