Circuit aging simulation is seen as a true enhancement to device and circuit simulation. To predict aging of circuit performance, tested models for device parameters are needed in which the change in device behavior as function of time, given the biasing and temperature condition of the device in the circuit, is correctly modeled. The time scale here is the lifetime of the product. A circuit simulator in the transient mode can predict circuit aging using a transformation of the dc/ac biasing situation with an appropriate scaling mechanism. Device aging models that can be implemented in such a circuit simulator are presented here for nMOS and DMOS (double diffused MOS) based on measurements and empirical modeling.