A semiconductor device includes a substrate including a cell active region and a peripheral active region, a direct contact arranged on a cell insulating pattern formed on the substrate and connected to the cell active region, a bit line structure including a thin conductive pattern, contacting a top surface of the direct contact and extending in one direction, and a peripheral gate structure in the peripheral active region. The peripheral gate structure include a stacked structure of a peripheral gate insulating pattern and a peripheral gate conductive pattern, the thin conductive pattern includes a first material and the peripheral gate conductive pattern include the first material, and a level of an upper surface of the thin conductive pattern is lower than a level of an upper surface of the peripheral gate conductive pattern.