Hot-carrier-induced degradation of NMOST with large periodic drain-source signal is considered. A general lifetime model for large periodic drain signal is derived assuming quasi-static approximation, starting from a lifetime model in DC conditions. Two practical cases are discussed: large sinusoidal drain signal from 0 V to V-DD (circuit supply) and trapezoidal signal from 0 V to V-DD (in special case, it reduces to triangular waveform). Compact, practically useful formulas are proposed for AC/DC lifetime ratio. The model for AC conditions is based on the same physical approximations that are traditionally used in the derivation of the physically crude, but well applicable lifetime models in DC conditions. Finally, a strategy is proposed for building-in HC-reliability of NMOSFET that is subjected to periodic large drain-signals in analog circuits. (c) 2006 Elsevier Ltd. All rights reserved.