In this paper, we propose a closed form expression of a new and accurate analytical substrate current model for both pre-stressed and post-stressed MOSFET's. It was derived based on the concept of effective electric field, which gives a more reasonable impact ionization rate in the lucky-electron model. This effective electric field, composed by two experimentally determined parameters, can be regarded as a result of nonlocal heating effects within devices. This model shows a significant improvement to the conventional local field model. One salient feature of the present model is that it allows us to characterize the time evolution of the substrate current of stressed MOSFET's for the first time. Experimental verification for a wide variety of MOSFET's with effective channel lengths down to 0.3µm shows that the new model is very accurate and is feasible for any kind of MOS device with different drain structures. The present model can be applied to explore the hot carrier effect in designing submicrometer MOS devices with emphasis on the design optimization of a device drain engineering issue. In addition, the present model is well suited for device reliability analysis and circuit level simulations.