This paper presents a new approach to improve the speed of switch-level timing simulation of MOS digital circuits. High performance is achieved by redefining the concept of event within the event-driven selective-trace paradigm. Unlike conventional techniques, in our approach an event occurs on an input slope change rather than a voltage change, thereby, lessening significantly the number of events to be treated during the simulation. The accuracy of this approach is improved by taking into account temporal proximity of multiple input transitions. Experimental results obtained for several circuits show significant speed-up compared to conventional switch-level timing simulation techniques.