In this work, we present an experimental and theoretical study of nitride-trap devices with a HTO/Al2O3 bi-layer blocking oxide. Such (Silicon/Alumina/HTO/Nitride/Oxide/Silicon) SAONOS devices are compared with standard (Silicon/HTO/Nitride/Oxide/Silicon) SONOS and (Silicon/Alumina/Nitride/Oxide/Silicon) SAWS memories. The role of the different layers (blocking oxide and control gate) is deeply analyzed, focusing on their impact on memory performance and reliability. Then, a semi-analytical model is developed, which provides a good understanding of the physical mechanisms at the origin of program/erase characteristics. (C) 2009 Elsevier Ltd. All rights reserved.