A semiconductor memory device may include a substrate, a bit line extending in a first direction on the substrate, a first word line and a second word line extending in a second direction to cross the bit line, a back-gate electrode extending in the second direction between the first word line and the second word line, first and second active patterns disposed between the first and second word lines and the back-gate electrode and connected to the bit line, contact patterns coupled to the first and second active patterns, respectively, a first back-gate capping pattern between the contact patterns and the back-gate electrode, and first gate capping patterns between the contact patterns and the first and second word lines. The first back-gate capping pattern and the first gate capping pattern may have first and second seams, which are extended in the second direction and are located at different vertical levels.