The photocurrent kinetic response and the photocurrent spectral response at 300 K are reported for Bi12SiO20in the optical range 1.0–2.0 eV. In this range trap occupancy dominates the response. The kinetic response of the transient‐trap‐filled photocurrent provides values of the electron trap density and the optical absorption coefficient for the photoionization of the electron trap. The optical ionization energies of the traps are provided from the trap‐filled spectral response. Combining these quantities with previously determined thermal ionization energies of the electron traps provides a value for the electron effective mass of m*=14 m and a value for the effective density of states in the conduction band ofNc=1×1017T3/2. Using this value for the effective mass, an optical absorption coefficient for the photoionization process is calculated, and found to be in good agreement with the experimentally observed value.