A method for fabricating semiconductor device is disclosed. First, a substrate is provided, and a first dielectric layer is formed on the substrate, in which a first conductor is embedded within the first dielectric layer. Next, a second dielectric layer is formed on the first dielectric layer, part of the second dielectric layer is removed to form a contact hole, and a lateral etching process is conducted to expand the contact hole to form a funnel-shaped opening. Next, a metal layer is formed in the funnel-shaped opening, and the metal layer is planarized to form a second conductor.