Insulated Gate Bipolar Transistor (IGBT) devices, during the Unclamped Inductive Switching (UIS) process, are subjected to extreme high voltage and large current simultaneously, which can easily lead to avalanche failure. Avalanche ruggedness is a measure of the device’s ability to withstand such extreme conditions. This paper investigates the failure mechanisms and avalanche robustness of IGBT devices under overvoltage conditions, both in static avalanche and dynamic avalanche during the turn-off process, through theoretical analysis, analytical modeling, and numerical simulation. Furthermore, the influence of temperature on the dynamic and static avalanche breakdown characteristics is studied. The results show that the causes of both dynamic and static avalanche breakdown are the internal electric field of the device reaching the avalanche critical breakdown field, triggering the avalanche multiplication effect of internal carriers. The occurrence of avalanche multiplication does not necessarily mean device failure. However, when the energy generated during the avalanche voltage maintenance phase exceeds the device’s avalanche ruggedness, the device undergoes destructive avalanche breakdown failure. The current density distribution inside the device changes compared to before failure, the parasitic transistor turns on, and gate latch-up occurs, making the device unable to turn off normally. Increased temperature leads to a higher avalanche breakdown voltage, shorter avalanche voltage maintenance time, increased power dissipation during avalanche, and reduced avalanche ruggedness, affecting the turn-off reliability of the device.