In this study, Anodic Aluminum Oxide (AAO) is used as the storage layer instead of silicon nitride in a silicon-SiO2-Si3N4-SiO2-Silcon (SONOS) structure in flash memory devices and a double I-V method is utilized to investigate its charge trapping behavior on SiO2-Al2O3-SiO2 (OAO) triple stacks. The experimental results show that more initial charge density can be charged into the centroids of neutral charge trapping sites using post deposition annealing (PDA) treatment in OAO triple stacks. Under stress bias testing, OAO triple stacks exhibit a larger shift of threshold voltage than do ONO type devices. The trap energy levels of the bulk electron traps in high k AAO materials were determined. The initial trapping charges are produced during the fabrication process and are changed into centroids of neutral charge trapping sites after PDA treatment, which are responsible for charge trapping/de-trapping during programming/erasing. All devices show that the trapping centroid moves to the top oxide with an increase of stress time. (C) 2009 Elsevier Ltd. All rights reserved.