A semiconductor device manufacturing method according to the exemplary embodiments of the disclosure includes patterning a substrate, thereby forming an active pattern, forming a trench penetrating the active pattern, forming a support layer covering the trench, forming a first opening at the support layer, forming a gate electrode layer filling the trench through the first opening, and forming a bit line structure electrically connected to the active pattern. The support layer includes a base portion covering a top surface of the active pattern, and a support disposed in the trench.