The miniaturization of integrated circuits has made microelectronics devices better and better whether in terms of integrability, speed or cost. One of the drawbacks of this trend is that the devices are more and more prone to failure caused by unwanted electrical stresses, as power density increases. This has gone to the point where half of the available area is sometimes used for protecting the active device. In general, the protection also hinder the performance of the device. The first type of unwanted stress whose effects have been studied in this thesis is electrostatic discharge (ESD). ESD effects on Silicon-Germanium hetero-junction bipolar transistors (SiGe HBT) used in low noise amplifiers have been studied. Two different types of athermal failure behaviors have been identified and explained in terms of silicon breakdown for long rise time and transistor parasitic action for short rise time and/or substrate coupling. Two types of Silicon controlled rectifiers (SCR) used as ESD protection were studied. The SCR action was studied in terms of initial triggering, on-state spreading (OSS) in one finger, and sequential finger triggering was studied using Transient Interferometric Mapping (TIM). The role of trigger taps was investigated in breakdown with Emission Microscopy (EMMI) and during triggering using TIM. The reliability of Gallium Nitride High Electron Mobility Transistors (GaN HEMTs) has been investigated in terms of vertical breakdown, degradation of the conducting and blocking performance at high temperature and short circuit load conditions. The behavior of HEMT devices under pulsed stress conditions (ESD and short circuit load) was studied with the TIM technique, which allows to probe the heat dissipation and the free carrier concentration through their effect on the refractive index of the material. New methods to analyze of the phase shift were developed, also enabling to work with distorted signal, or indirect probing outside the active region.