A physically unclonable function (PUF) device includes a memory cell array including a plurality of memory cells, a selecting circuit configured to select one or more memory cells among the plurality of memory cells in response to a challenge, and a sense amplifier and quantizer configured to generate a quantize signal from the selected memory cell. The number of quantization sections for generating the quantize signal may be different from the number of resistance state distributions generated from the selected memory cell. One or more quantization sections may exist in one resistance state distribution section.