We describe a biochip based on an integrated circuit photodiode array for use in medical diagnostics. The biochip is a self-contained device which has photosensors, amplifiers, discriminators and logic circuitry on board. The development and evaluation of various microchip system components of the genosensor are discussed. The performance of the DNA biochip device is illustrated with fluorescence detection of DNA probes specific to gene fragments of the human immuno-deficiency virus 1 (HIV1) system. The usefulness and potential of the DNA biochip technology for rapid and cost-effective medical diagnostics is discussed.