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We investigate the effect of elevated ambient temperature on thermal breakdown (TB) modes in linear-geometry electrostatic discharge (ESD) protection n-p-n transistors of smart power technology subjected to 0.5-1- μs-long ESD pulses. The current transport in these devices has a form of traveling current filaments (CFs) where TB at room temperature occurs at one of the device ends. An increase in ambient temperature gives rise additionally to another failure mode, inside the device. For the failure mode at the device end, the increase of ambient temperature in the range up to 100°C causes shortening of the averaged time to TB 〈tTB〉 by a duration that the CF needs for one round trip over the device width. At ambient temperatures up to 180°C, the TB may occur even at initial triggering CF position inside the device, before the CF starts to move. The ambient temperature at which the transition between CF modes with different 〈tTB〉 occurs is investigated as a function of stress current. Furthermore, inspecting the failure current of devices with different widths shows that there is an equivalence between the effect of increased ambient temperature and the effect of the preheating at the device end by a previous CF passage. The experiments are supported by 3-D thermal simulation of temperature in moving and standing CFs.