A semiconductor device includes a substrate having a trench, a bit line in the trench, a first spacer extending along the trench and at least a portion of a side surface of the bit line and in contact with the bit line, and a second spacer disposed within the trench on the first spacer. The bit line is narrower than the trench, and the first spacer includes silicon oxide. A method of forming a semiconductor device includes forming a trench in a substrate, forming a bit line within the first trench of width less than that of the first trench, and forming a first spacer that lines a portion of the trench and includes silicon oxide in contact with at least a portion of a side surface of the bit line, and forming a second spacer over the first spacer in the trench.