A new photovoltaic characteristic of porous silicon(PS)is reported in this paper.The PS layer was prepared by anodization of

p

-type Si single cryatal wafers in HF aqueous solution at current density of about 10mA/cm

2

.When the PS layer was irradiated by light

an intense photo-electromotive force was generated on the sample.The potential of PS layer is higher than that of substrute.The photocurrent was inereased with increasing illuminance.There was no any photoelectromotive force on a

p

-type Si single crystal wafer when it was irradiated with light.These facts demonstrat that the photovoltaic effect is originated in PS layer.This effect was also observed on samples formed by

n

-Si single crystal wafers.