Thermal runaway
From sciforums_encyclopedia
a destructive process of transistor conductance that can be eliminated by better circuit design. basically when a transistor conducts it produces a slight increase in the temperature of the material. a higher temperature results in increased current flow which leads to a higher temperature. if no means of limiting current is built into the circuit design the above process continues until the transistor is destroyed. germanium transistors are more prone to thermal runaway than silicon.