As integrated circuits are getting more and more complex, they are becoming increasingly vulnerable to transient disturbances (e.g. to electrostatic discharges, ESD). The development approaches for on-chip ESD protection devices often have a very experimental character: ESD designers make use of trial-and-error procedures to evaluate many variations of protection structures. This methodology is very time-consuming, as it can require several redesigns to find proper ESD protection devices for a given process technology. Also, from one process generation to the next, already well-established ESD structures may completely change their ESD behavior. Now, more sophisticated design approaches make use of TCAD-based techniques. Simulations of ESD circuits provide a deeper understanding of the functionality of their protection behavior. In this paper we show how such simulation techniques have been successfully used to design an efficient trigger-circuit for SCR, a specific class of very powerful ESD protection devices.