A manufacturing method of a semiconductor device is provided. A substrate is provided. The substrate has an active area. A plurality of word lines are formed on the substrate. Each of the word lines is extended along a first direction, and the word lines are arranged on both sides of the active area along a second direction. A first dielectric layer is formed on the substrate. The first dielectric layer covers the active area and the word lines. A contact is formed on the active area. The contact penetrates through the first dielectric layer and is electrically connected to the active area. A heating process is performed on the first dielectric layer to shrink the first dielectric layer inward, and the contact is correspondingly expanded outward.