Semiconductor devices and manufacturing and design methods thereof are disclosed. In one embodiment, a semiconductor device includes an active FinFET disposed over a workpiece comprising a first semiconductive material, the active FinFET comprising a first fin. An electrically inactive FinFET structure is disposed over the workpiece proximate the active FinFET, the electrically inactive FinFET comprising a second fin. A second semiconductive material is disposed between the first fin and the second fin.