Abstract: This paper reviews the application of plastic encapsulated devices in fields requiring high reliability, and the burn-in tests to check its reliability, with emphasis on the impacts of the increase of leakage currents and parameter variations accompanied with the improvement of integration extent and processing technology, which would become crucial where stressed voltage and temperatures are applied. Therefore, it is very important to carry out thermal stability study in the burn-in tests of plastic encapsulated device in order to achieve high reliability.