Semiconductor devices and semiconductor cell arrays are provided herein. In some examples, a semiconductor device includes a multi-fin active region, a mono-fin active region, and an isolation feature between the multi-fin active region and the mono-fin active region. The multi-fin active region includes a first plurality of fins, a second plurality of fins parallel to the first plurality of fins, a first n-type field effect transistor (FET), and a first p-type FET. The mono-fin active region abuts the multi-fin active region. The mono-fin active region includes a first fin, a second fin different from the first fin, a second n-type FET, and a second p-type FET. The isolation feature is parallel to the first and second gate structures.