We report experimental observations and theoretical modeling of an unusual photoelectric effect in deoxyribonucleic acid (DNA) thin-film devices, under visible and near-infrared illumination. The devices also show diode-type rectifying current-voltage (I-V) characteristics. An equivalent circuit model was constructed that fits the experimental data, and physical processes likely to arise in the devices are discussed. We envisage the formation of a Schottky barrier at the DNA film-metal interface and infer that the photoresponse arises from photoinjection of electrons from the metal into the DNA film. © 2009 SPIE.