In the minimal supersymmetric standard model, large left-right mixing of stau’s is sometimes intriguing from phenomenological viewpoints. However, too large left-right mixing is not acceptable since the electroweak-breaking vacuum becomes metastable. In this talk the vacuum transition rate is evaluated by using semiclassical techniques, and constraints on parameters of the model are shown. In the calculation the bounce solution is derived in the multifield space. These constraints are also applied to the case of the low-energy minimal gauge mediation model.