In this letter, we point out the methodological problem of the conventional temperature-accelerated life-test method of nand Flash memory. We confirm that the generally assumed Arrhenius law is inconsistent with extrapolation of data-retention time-to-failure of nand Flash memory since several failure mechanisms come up together. For the first time, we completely separated three main failure mechanisms and extracted each activation energy (Ea) in 21-nm nand Flash memory. From the results, we assured that each failure mechanism follows the Arrhenius law. In order to estimate the lifetime of nand Flash memory accurately, each failure mechanism should be considered.