Drain source voltage represents the maximum voltage that can be applied across the drain and source terminals of a power transistor under turn-off conditions. When the applied voltage across the drain and source terminals exceeds the limit, it causes the power transistor to enter the breakdown region.

In the breakdown region, the power transistor has a high drain current due to the avalanche multiplication of electrons. At high drain-source voltage, the electric field exerts on the electrons and frees them from covalent bonds of the silicon atom. These free electrons move with high velocity and collide with other atoms resulting in more free electrons creation. This results in the phenomenon of avalanche multiplication of electrons.