In a method of forming a semiconductor device including a fin field effect transistor (FinFET), a sacrificial layer is formed over a source/drain structure of a FinFET structure and an isolation insulating layer. A mask pattern is formed over the sacrificial layer. The sacrificial layer and the source/drain structure are patterned by using the mask pattern as an etching mask, thereby forming openings adjacent to the patterned sacrificial layer and source/drain structure. A dielectric layer is formed in the openings. After the dielectric layer is formed, the patterned sacrificial layer is removed to form a contact opening over the patterned source/drain structure. A conductive layer is formed in the contact opening.