This work presents an extensive study on the effects of Electrostatic Discharges (ESD) on state-of-the-art GaN based LEDs, based on optical and electrical measurements carried out during the ESD events. ESD events were simulated through a Transmission Line Pulser (TLP) which generates voltage pulses with a duration of 100 ns and increasing amplitude: during each pulse, spatially-resolved electroluminescence measurements were carried out through an high speed EMCCD camera. These measurements allowed to identify the chip region where the discharge is localized and the change in the damaged area induced by consecutive ESD events. Also the current and voltage waveforms at the LED terminal were monitored during the tests; this analysis provided important information about modifications the impedance of the devices. The analysis was carried out on different types of commercially available low-power GaN-based LEDs with several differences in the manufacturing technology. Thanks to these tests we have identified two different failure behaviours during a destructive ESD event, clearly related to the different defects in the semiconductor lattice and to structure of the chip. (C) 2014 Elsevier Ltd. All rights reserved.