One of the biggest advantages of the IGBT, is its inherent capability to limit the external current in case of a short-circuit event. Until now, the failure mechanism that limits the short-circuit capability of high voltage buffer-type IGBTs has not been fully understood. The experimental data show that the most common short-circuit failure type cannot be explained by any known failure mechanism such as cell latch-up, avalanche breakdown or thermal runaway. The goal of this thesis was to find the destruction mechanism that limits the short-circuit capability of the investigated high voltage IGBTs. This was achieved by using a combination of device simulations and experimental investigations of3.3kV, 4.5kV and 6.5kV IGBTs.