A physically unclonable function unit includes and anti-fuse transistor and a control circuit. The anti-fuse transistor has a first terminal, a second terminal, and a gate terminal. The control circuit is coupled to the anti-fuse transistor. During an enroll operation, the control circuit applies an enroll voltage to the gate terminal of the anti-fuse transistor and applies a reference voltage to the first terminal and the second terminal of the anti-fuse transistor. The enroll voltage is higher than the reference voltage, and is high enough to create a rupture path on the gate terminal to the first terminal or to the second terminal.