A semiconductor memory device includes word lines extending in a first direction on a semiconductor substrate, bit line structures crossing over the word lines and extending in a second direction intersecting the first direction, and contact pad structures between the word lines and between the bit line structures in plan view. A spacer structure extends between the bit line structures and the contact pad structures. The spacer structure includes a first air gap extending in the second direction along sidewalls of the bit line structures and a second air gap surrounding each of the contact pad structures and coupled to the first air gap.