The author has proposed a new device structure-GaAs-based Schottky-senticonductor-ohmic (SSO) photodiode. SSO photodiodes of various sizes, from 20 x 20 mum(2) to 200 x 200 mum(2) were fabricated. The influence of the finger width and spacing on the leakage current and turn-on voltage were studied. The SSO photodiode was observed to have distinctly higher optical sensitivity during the forward-bias compared to the PIN diode. From the present study, the author concludes that the SSO photodiode has good potential to be used as an optically controlled switch. (C) 2002 Elsevier Science Ltd. All rights reserved.