Provided may be a semiconductor memory device and a method of forming the semiconductor memory device. The memory device of example embodiments may include a bit line structure including a bit line on a semiconductor substrate, and a buried contact plug structure including a buried contact pad and a buried contact plug that extends in a lower portion of the bit line from one side of the bit line and connected to the buried contact pad. A width of the buried contact plug near a top surface of the buried contact pad may be greater than a width of the buried contact plug adjacent to the bit line.