The low‐temperature four‐wave mixing (FWM) photorefractive response was investigated in undoped Bi12GeO20 (BGO) crystals. The FWM diffraction efficiency increases as the temperature is lowered until a local maximum is reached after which it decreases. The temperature where the maximum intensity FWM signal occurs depends on the write conditions. A model assuming both electron and hole gratings was used to describe the observations. Two shallow trap levels of 0.015 and 0.08 eV were identified as being responsible for the fast decay (≪1 s) components of the FWM signal in undoped BGO.