Definition: thermal runaway
A repeating cycle in which excessive heat causes more heat until the operation ceases or an explosion occurs. For example, lithium ion batteries have been known to exhibit thermal runaway and explode. In germanium-based bipolar transistors, high temperatures cause current to leak. This, in turn, causes the transistor to heat even more and eventually become unstable or self-destruct. Obviously, after thermal runaway appears in new systems, the product is re-engineered to prevent it.