A structure of semiconductor device includes a substrate. A first dielectric layer is disposed over the substrate, wherein the first dielectric layer has an air trench. A plurality of trench metal layers is disposed in the first dielectric layer, wherein the air trench is between adjacent two of the trench metal layers and without contacting to the trench metal layers. A liner layer is disposed on the first dielectric layer to cover the trench metal layers and a profile of the air trench. An etching stop layer is disposed on the liner layer, wherein the etching stop layer seals the air trench to form an air gap between the adjacent two of the trench metal layers.