Abstract: In accordance with an embodiment, a physically unclonable function device includes a set of transistor pairs, transistors of the set of transistor pairs having a randomly distributed effective threshold voltage belonging to a common random distribution; a differential read circuit configured to measure a threshold difference between the effective threshold voltages of transistors of transistor pairs of the set of transistor pairs, and to identify a transistor pair in which the measured threshold difference is smaller than a margin value as being an unreliable transistor pair; and a write circuit configured to shift the effective threshold voltage of a transistor of the unreliable transistor pair to be inside the common random distribution.