Abstract: A semiconductor device and a method for manufacturing an interconnecting metal layer thereof are provided. The semiconductor device includes a gate layer, a dielectric layer, an insulating layer, an epitaxial layer, and a sidewall liner. The dielectric layer is disposed on one side of the gate layer, the insulating layer is disposed on another side of the gate layer, the epitaxial layer is located on the insulating layer, and the sidewall liner penetrates the dielectric layer and the gate layer, and one end of the sidewall liner is connected to the epitaxial layer. The sidewall liner is converted from a high-k material to a low-k material by hydrogen and oxygen plasma treatments.