Infrared detection was accomplished with the narrow bandgap semiconductor (∼0.1 eV), ReSi2. Photoresistors were fabricated from a polycrystalline ReSi2film grown on a silicon substrate. A light‐induced decrease in resistance was observed, which was due both to film photoconductivity and to a light‐sensitive contact resistance. The relative spectral response (measured at 10 K) in the wavelength range from 3000 to 6000 nm roughly follows the number of photons absorbed as estimated from the optical absorption coefficient of ReSi2. Thus, the sample is aquantum, rather thanthermal, detector. The mechanism of detection is believed to be the intrinsic band‐to‐band photogeneration of excess free carriers, leading to photoconductivity and to the reduction in contact resistance. It is suggested that ReSi2offers the potential for a new intrinsic semiconductor infrared detector technology, which may be integrated on a silicon chip, and whose absorption edge is well into the far‐infrared range. ©1995 American Institute of Physics.