A device is provided. The device includes a physical unclonable function (PUF) cell array. The PUF cell array includes multiple bit cells, and generates a PUF response output, in response to a challenge input, based on a data state of one bit cell in the bit cells. Each of the bit cells stores a bit data and includes a transistor having a control terminal coupled to a word line and a first terminal coupled to a source line, a first memory cell having a first terminal coupled to a first data line and a second terminal coupled to a second terminal of the transistor, and a second memory cell having a first terminal coupled to a second data line, different from the first data line, and a second terminal coupled to the second terminal of the first memory cell at the second terminal of the transistor.