This paper introduces an approach of extracting process variations inside System-on-Chips (SoCs) to derive a Physical Unclonable Function (PUF). The process variations are extracted from the architecture of a Digital-to-Analog Converter (DAC). The DAC consists of two independent resistive ladders to provide one single or two output voltages. The resistive ladder is characterized by the SoC with the on-chip Analog-to-Digital Converter (ADC) module. The developed PUF concept that exploits the process variations of the DAC is described and evaluated in this work. Due to the concept of not accepting an input challenge to the PUF, we designed a so-called weak-PUF. The final generated PUF response or also called fingerprint has a total length of 652 bits when using the maximum number of possible positions. In a typical operation condition, a worst-case intra-Hamming Distance (HD) of approximately 5% is achieved. Over a wide temperature range of -10°C to 70°C the intra-HD is increased to 13% in the worst-case. The inter-HD for all observed operating conditions is approximately 46%.