Charge trapping characteristics of ultrathin silicon dioxide NOD films during constant voltage stress (CVS) in direct tunneling regime have been presented. Both bulk and border traps have been segregated from oxide trapped charges. Our measurement results indicate that electron trapping in as fabricated traps in ultrathin samples was suppressed and/or absent during prolonged stress. In addition, the generation kinetics of "border" and "bulk" trapped positive oxide charges have been studied. From the bulk oxide charge relaxation experiments, nature of as-fabricated intrinsic hole traps in SiO2 has been determined. Our results show that both bulk and border trapped positive oxide charges are mostly contributed by proton related species possibly the [Si-2=OH](+) centers. Based on experimental observations, a physical model of stress-induced bulk positive charge generation/trapping has been proposed. (c) 2007 Elsevier Ltd. All rights reserved.