Abstract: In this paper,the breakdown characteristics of the double-gate junctionless transistor is simulated using the 2-D device simulator,Medici. The electric field distribution and the integration of impact ionization rate is analyzed. The results show that the breakdown mechanism of double-gate junctionless transistors is still avalanche breakdown. Furthermore,the influence of the channel length,channel doping concentration and gate voltage on the breakdown voltage is investigated in detail. The simulation indicates that the breakdown voltage of a double-gate junctionless transistor increases linearly with the increase of the channel length and channel doping concentration. On the contrary,a light decrease of breakdown voltage can be found when the gate voltage increases.