We demonstrate electric bistability induced by the positive feedback of self-heating onto the thermally activated conductivity in a two-terminal device based on the organic semiconductor C(60). The central undoped layer with a thickness of 300 nm is embedded between thinner n-doped layers adjacent to the contacts, minimizing injection barriers. The observed current-voltage characteristics follow the general theory for thermistors described by an Arrhenius-like conductivity law. Our findings include hysteresis phenomena and are of general relevance for the entire material class since most organic semiconductors can be described by a thermally activated conductivity.