THERMAL RUNAWAY
What do you think what is thermal runaway?
Our electronic definitions web site has answer for that as well:



thermal runaway

as a transistor heats, its junction temperature increases. This increases the collector current, which forces the junction temperature to increase further, producing more collector current, etc., until the transistor is destroyed.


Another definition of thermal runaway:
as a transistor heats, its junction temperature increases. This increases the collector current, which forces the junction temperature to increase further, producing more collector current, etc., until the transistor is destroyed.