A method of forming a FinFET device includes following steps. A substrate is provided with a plurality of fins thereon, an isolation layer thereon covering lower portions of the fins, a plurality of dummy strips across the fins, and a dielectric layer aside the dummy strips. The dummy strips is cut to form a trench in the dielectric layer. A first insulating structure is formed in the trench, wherein first and second groups of the dummy strips are beside the first insulating structure. A dummy strip is removed from the first group of the dummy strips to form a first opening that exposes portions of the fins under the dummy strip. The portions of the fins are removed to form a plurality of second openings below the first opening, wherein each second opening has a middle-wide profile. A second insulating structure is formed in the first and second openings.