A mechanism for current interruption in a collisionless plasma is proposed. When a current exceeds the Buneman instability threshold, the instability leads to the growth of Bernstein-Greene-Kruskal (BGK) waves in the form of a row of solitary negative potential wells along the current path. As these solitary BGK waves grow, they trap an increasing number of current-carrying electrons between neighboring potential wells. This trapping process is proposed as a possible mechanism for current interruption in a collisionless plasma. The trapping is complete in about 100 plasma periods, as is indicated by a number of numerical simulation results. The fraction of current interrupted by the proposed mechanism depends on the ratio of the ion thermal energy to the electron streaming energy. In a model examined in this paper it is found that for the unstable current to be interrupted and reduced to one half of its original value, the ion to electron energy ratio must be greater than 2. To interrupt the current by a larger fraction, a higher energy ratio is required. Possible application of this current interruption mechanism to magnetospheric substorms is suggested.