Measurements of low frequency shot noise due to photoinduced currents have been carried out on planar molybdenum/n-type silicon/molybdenum structures having long neutral region and Schottky barriers at both ends. Measurements were performed in the frequency range between 1 and 200 kHz at room temperature. The observed shot noise was found to be lower than the level of full shot noise. That is, when the current noise is expressed as S(omega) = 2qIGamma(2) (q, the electronic charge; I, the average current), the noise factor, Gamma(2), was estimated to be around 0.9, which is smaller than unity corresponding to so-called full shot noise. These results are attributed to the decay of autocorrelation effect in the current component photoinduced in the neutral region. (C) 2002 Elsevier Science Ltd. All rights reserved.