Avalanche breakdown is a phenomenon in semiconductor devices where, under a high reverse voltage, the electric field becomes strong enough to accelerate free electrons to high energies. These energetic electrons collide with atoms in the lattice, freeing more electrons and creating a chain reaction. This sudden multiplication of charge carriers leads to a rapid increase in current, causing the device to conduct heavily. Avalanche breakdown is commonly observed in diodes and transistors, and while it can damage devices if uncontrolled, it is also harnessed in avalanche diodes for voltage regulation and detection applications.