A security device includes a physical unclonable function (PUF) cell array including PUF cells connected with word lines and bit lines; first decoder circuitry connecting a first bit line connected to a target PUF cell with a first data line and a second bit line connected with a reference PUF cell to a second data line; a digital-to-analog converter (DAC) control circuit outputting first and second digital codes; a first DAC between a power supply voltage and the first data line, the first DAC generating a first analog output in response to the first digital code; a second DAC between the power supply voltage and the second data line, the second DAC generating a second analog output in response to the second digital code; and a sense amplifier comparing the first analog output and the second analog output and outputting a comparison result.