In this paper, we present a thorough investigation of the physical and electrical characteristics of a SiO2/Al2O3/SiO2 (OAO) stack film. The crystallization temperature of an aluminum oxide (Al2O3) material of 9.2 nm thickness is about 925 °C, and leakage current is determined by trap-assisted tunneling (TAT) in the low E-field region owing to grain boundary formation. Nevertheless, crystalline Al2O3 can increase dielectric constant, lower band gap, and cause offset of conduction band (Δ EC); thus, a lower leakage is obtained in high E-field region. Comparing various films with the scheme of SiO2/Al2O3/SiO2 and presented at various post deposition annealing (PDA) temperatures, it is found that the top oxide thickness and crystallization temperature of the Al2O3 material play key factors for high electric strength and electron trapping. Our experiment demonstrated that a specific SiO2/Al2O3/SiO2 stack film incorporated with an appropriate thermal budget for Al2O3 annealing can be utilized for future NAND flash memory cells.