Thin‐film junctions of ZnO‐Bi2O3have been made by sputtering. The junction breakdown voltage ranges from 2.3 to 3.0 V when ZnO is positively biased. A negative resistance usually appears after the breakdown. When ZnO is negatively biased, the current is proportional to an exponential function of the applied voltage with a built‐in barrier of roughly 0.8 V. These characteristics and their temperature dependence on being cooled down to 77 °K will be discussed in terms of a qualitativen‐nheterojunction with interface states.