In this study, we investigated the thermally transferred optically stimulated luminescence (TT-OSL) characteristics of BeO ceramic plates with and without annealing treatment, focusing on the effects of preheating temperature and irradiation history. OSL and TT-OSL measurements were performed after X-ray irradiation at doses of 1, 5, and 10 Gy. The OSL intensity reached a maximum at a preheating temperature of approximately 250 ℃, showing a significant enhancement particularly in the low-dose region. This enhancement was attributed to the thermal transfer of electrons from deep traps to shallow optically active traps. Even after annealing at 1000 ℃, which completely erased the irradiation history, TT-OSL signals were observed, indicating that deep traps were reoccupied upon reirradiation and thermally activated during preheating. The results revealed that the TT-OSL characteristics of BeO ceramics are governed by a dual process: the thermal transition of electrons from deep traps to shallow optically active traps and the thermal depletion of initially active traps. Because this dual process depends strongly on the irradiation history, it significantly affects measurement accuracy and sensitivity. Therefore, proper annealing and thermal management are essential for achieving stable and precise dose measurements using BeO-based OSL dosimeters.