A memory system includes a memory array comprising a plurality of memory cells. Each of the memory cells includes a first programming transistor, a second programming transistor, a first reading transistor coupled to the first programming transistor in series, and a second reading transistor coupled to the second programming transistor in series. The memory system includes an authentication circuit operatively coupled to the memory array. The authentication circuit is configured to generate a Physically Unclonable Function (PUF) signature based on respective logic states of the plurality of memory cells. The logic state of each of the plurality of memory cells is determined based on a preceding breakdown of either the corresponding first programming transistor or second programming transistor.