Light emission from Si MOSFET's operating in the saturation region is observed. This observation provides direct evidence for the phenomenon of photocarrier generation in the substrate of VLSI's. The light emission appears to be uniform along the device width and emanates from the drain end of the MOSFET under normal operation. Light spots of much higher intensity are observed when the device is biased into the snap-back regime. This provides insights into the mechanism of snap-back breakdown.