The paper introduces the concept of chaos in the sense of semigroup action.It is showed that transitive and denseness of periodic points imply sensitive.

• 摘要引进了半群混沌作用的概念，证明了若半群S在紧致度量空间X上的连续作用满足拓扑可迁和周期点稠两个条件，则此作用满足对初值的敏感依赖性。