We present a monolithic CMOS-based biosensor system comprising an array of gold nanowires and the signal-conditioning circuitry on the same chip. Different numbers of parallel nanowires have been patterned on the chip via e-beam lithography and lift-off process after the CMOS fabrication. The on-chip circuitry monitors the resistance of the nanowires by applying a constant voltage and measuring the respective current. The analog signal is then digitized on chip and transmitted. The system has been successfully fabricated and tested. I-V curves of the bare nanowires as well as resistance changes for different gold nanowires after applying NaCl solution onto the chip are shown.