A semiconductor device includes a semiconductive substrate, a first semiconductive fin and a second semiconductive fin extending upwards from the semiconductive substrate, an isolation structure at least partially between the first semiconductive fin and the second semiconductive fin, a first semiconductive raised portion and a second semiconductive raised portion. The first semiconductive raised portion extends upwards from the semiconductive substrate, is buried under the isolation structure, and is between the first semiconductive fin and the second semiconductive fin. A top surface of the first semiconductive fin is higher than a top surface of the first semiconductive raised portion. The second semiconductive raised portion extends upwards from the semiconductive substrate, is buried under the isolation structure, and is between the first semiconductive raised portion and the second semiconductive fin.