Photoconductivity of vitreous semiconductors in the system As-S-Te was measured under illumination with white light (2870°K) as a function of illumination intensity, applied voltage and temperature. The resistance changed by a factor of 1.5 to 20 at the illumination intensity of 100 lux, and the ratio of the dark resistance to the resistance on illumination was proportional to about 1/5 th power of resistivities at room temperature. Photocurrent changed linearly with applied voltage. The relationship between photocurrent (IPh) and illumination intensity (E) was expressed by Iph=A•En with two different n values for an individual sample. The n value was about 1.0 at lower illumination intensities, and about 1/2 at higher intensities. This phenomenon implies that the recombination process varies with illumination intensities. Photocurrent varied exponentially as the reciprocal of the absolute temperature, and the activation energy for photoconduction ranged from 0.2 to 0.5 eV. The reason for such values of the activation energy being obtained is briefly discussed.