Nanocrystal (NC) memories are considered the most natural evolution of the Flash memory concept, thanks to charge storage in discrete nodes reducing the impact of stress induced leakage current (SILC) on cell reliability. To demonstrate the feasibility of this technology, a clear assessment of cell performances at array level and a quantitative estimation of reliability improvements with respect to standard Flash are essential. In this work we investigate the statistical properties of NC memories by studying cell array stress test (CAST) structures. Using field-accelerated retention experiments, we show that array characteristics are affected by SILC tails after heavy cycling, revealing anomalous cells in the array with increased conduction of the tunnel oxide after stress. However, our quantitative analysis shows that the statistical impact of tails (10(-6) to 10(-5)) is largely reduced as compared to conventional Flash arrays. The excellent SILC immunity found in our samples is finally discussed. (C) 2004 Elsevier Ltd. All rights reserved.