在模论中，一个环 上的左模 若可表为单模的直和，便称 为半单模。

本条目中的环皆有乘法单比特素 。对于右模，相应的陈述依然成立。

以下陈述彼此等价：

• 是单模的和。
• 是其单子模的和。
• 对每个子模 ，存在子模 使得 。

In mathematics, especially in the area of abstract algebra known as module theory, a semisimple module or completely reducible module is a type of module that can be understood easily from its parts. A ring that is a semisimple module over itself is known as an Artinian semisimple ring. Some important rings, such as group rings of finite groups over fields of characteristic zero, are semisimple rings. An Artinian ring is initially understood via its largest semisimple quotient. The structure of Artinian semisimple rings is well understood by the Artin–Wedderburn theorem, which exhibits these rings as finite direct products of matrix rings.