A large leakage current (IR) is observed at reverse bias (VR) in 3C-SiC p+-n diodes. This leakage current is caused by a high density of stacking faults (SFs). The temperature dependence of IR is studied in the temperature range from 100 K to 295 K. It turns out that IR is thermally activated for reverse voltages VR |170| V. We propose that within this voltage range IR originates from thermally assisted tunneling of electrons and holes from band-like states of the SFs into the conduction and valence band. For VR > |170| V, the thermal barrier is strongly reduced and direct tunneling dominates. These dependences are simulated in the framework of a simplified model.