A semiconductor device includes a gate electrode disposed on a fin, a gate spacer disposed on the fin and a sidewall of the gate electrode, a source/drain electrode disposed on the fin, and an air pocket structure interposed between the gate spacer and the source/drain electrode. The air pocket structure includes an air gap, a first sidewall, a top sealing, a second sidewall and a bottom sealing. The air gap is enclosed by the first sidewall, the top sealing, the second sidewall and the bottom sealing arranged in a clockwise sequence. The top sealing and the bottom sealing include the same material of an energy removable material.