This paper presents a comprehensive numerical modeling for the threshold-voltage transients of nitride-based memory devices during programming, erasing and data retention. The developed numerical tool self-consistently solves the Poisson, continuity and trapping equations in the nitride layer using a drift-diffusion formalism. The continuity equation has been discretized using the Scharfetter-Gummel scheme and a modified Gummel-map has been optimized to ensure fully convergence of the equations. The numerical model is able to describe the memory device operation for different gate bias regimes, therefore addressing both the program/erase and the retention conditions. Finally, numerical results are shown to carefully reproduce experimental data on template devices with different gate stack compositions, validating the physical assumptions and making the model a valuable tool for nitride memories investigation and design. (C) 2010 Elsevier Ltd. All rights reserved.