The transition of the barrier-type thyristor(BTH) from blocking to conducting-state occurs between two entirely contrary physical states with great disparity in nature.The physical effects and mechanisms of the transition are studied in depth.The features of the transition snapback point are analyzed in detail.The transition snapback point has duality and is just the position where the barrier is flattened.It has a significant influence on the capture cross-section of the hole and high-level hole lifetime,resulting in the device entering into deep base conductance modulation. The physical nature of the negative differential resistance segmentⅠ-Ⅴcharacteristics is studied.It is testified by using experimental data that the deep conductance modulation is the basic feature and the linchpin of the transition process.The conditions and physical mechanisms of conductance modulation are investigated.The related physical subjects,including the flattening of the channel barrier,the buildup of the double injection,the formation of the plasma, the realization of the high-level injection,the elimination of the gate junction depletion region,the deep conductance modulation,and the increase in the hole’s lifetime are all discussed in this paper. The transition of the barrier-type thyristor (BTH) from blocking to conducting-state occurrence between two entirely contrary to physical states with great disparity in nature. The physical effects and mechanisms of the transition are studied in depth. Features of the transition snapback point are analyzed in detail. transition snapback point has duality and is just the position where the barrier is flattened. It has a significant influence on the capture cross-section of the hole and high-level hole lifetime, resulting in the device entering into deep base conductance modulation. The physical nature of the negative differential resistance segment I-V characteristics is studied. It is testified by using experimental data that the deep conductance modulation is the basic feature and the linchpin of the transition process. The conditions and physical mechanisms of conductance modulation are investigated.The related physical subjects, including the flattening of the channel barrier, the buildup of the double injection, the formation of the plasma, the realization of high-level injection, the elimination of the gate junction depletion region, the deep conductance modulation, and the increase in the hole’s lifetime are all discussed in this paper.