Trapping center properties of bismuth silicon oxide (Bi12SiO20) single crystals were investigated by thermoluminescence (TL) measurements performed in the 50–400 °C temperature range. Experimental TL curve recorded at heating rate of 1 °C/s presented two overlapped peaks around 279 and 362 °C. The heating rate dependency of TL curve was also studied for heating rates between 1 and 6 °C/s. The measured TL curves were analyzed using curve fitting, initial rise and different heating rate methods. The results of analyses indicated that TL glow curve is composed by two peaks associated with two discrete trapping centers at 0.81 and 1.10 eV. The revealed trapping centers were associated with intrinsic defects in the Bi12SiO20 compound under the light of previously reported papers. An energy band diagram was also plotted to indicate possible transitions within the forbidden band gap.