A planar metal/semiconductor/metal structure with Schottky barriers at both ends has attracted much attention as a competitive photodetector in an optical signal processing system. We report the influence of operating conditions on the low frequency (100 Hz-2 MHz) optical response of molydenum/n-type silicon/molybdenum structure having a long undepleted neutral region. It was found that the spectra of the photoresponse of this structure displayed an appreciable change due to biasing conditions. An explanation for these results was given. Further, numerical simulations were performed using its equivalent circuit model. A good agreement between the simulated and observed results was obtained. (C) 2002 Elsevier Science Ltd. All rights reserved.