A FinFET device structure is provided. The FinFET device structure includes a fin structure formed over a substrate, and a first inter-layer dielectric (ILD) layer formed over the fin structure. The FinFET device structure includes a gate structure formed in the first ILD layer, and a first S/D contact structure formed in the first ILD layer and adjacent to the gate structure. The FinFET device structure also includes a first air gap formed on a sidewall of the first S/D contact structure, and the first air gap is in direct contact with the first ILD layer.