By the standard Si-CMOS process, several designs are investigated of low-operating-voltage light-emitting/receiving devices. Our forward-biasing Si-LED designs having power transfer efficiency higher than that of other reports using standard Si-CMOS process. The same device can be used as both an optical receiver and signal transmitter. Results of chip-to-chip and signal transmission tests have been presented and shown that the interdigitated structure can increase the active region in light emission and improve the response time and sensitivity of photodiode. Furthermore, we have demonstrated that the light emission can be enhanced by current density. (c) 2005 Elsevier Ltd. All rights reserved.