The ever more decreasing size of power electronics is going to obtain devices always more compact and with a direct correlated consequence of higher heat fluxes obtained. After a first introduction to power electronics devices (classification, applications, market size,...) are analyzed the related heat losses causes and the failure types with the aim to start the study of thermal aspects. Indeed to stabilize the temperature below a maximum threshold of safety up to now were used different air and liquid cooling systems (indirect single and two-phase) that are in this work reviewed from the historical ones applied to electronics devices up to those used in our decade.