In this paper, a behavioral modeling methodology to predict ElectroStatic-Discharge (ESD) failures at system level is proposed and validated. The proposed models enable time domain simulation to determine voltage and current waveforms inside and outside an IC during ESD events in order to predict the susceptibility of an electronic system to ESD. Very-high-speed integrated circuit Hardware Description Language - Analog and Mixed Signals (VHDL-AMS) is used as the description language. The purpose of this methodology is based on the improvement of Input Output Buffer Information Specification (IBIS) models widely used in signal integrity (SI) simulation. In this paper the additional information required to be added to IBIS files is described, and comparison between simulations and measurements are exposed.