This paper deals with the experimental characterization of modern semiconductor devices under realistic operational conditions. First, a method for monitoring their thermal evolution as a response to transient electrical stimuli is presented. The proposed solution belongs in the category of optical infrared methods and offers good time and space resolution. In line with the requirements of leading-edge research and development activities, it is also characterized by a high-degree of versatility, which makes it a powerful tool in many diverse lines of investigations. Then, examples of the critical operation of modern-generation low-voltage power transistors are discussed. The cases proposed are selected from an actual application scenario and well demonstrate, on the one side, the need for accurate characterization of the components and, on the other side, the validity of the chosen solution.