A DRAM device includes an isolation region defining source and drain regions in a substrate, a first bit line structure connected to the source region, a second bit line structure disposed on the isolation region, an inner spacer vertically extending on a first sidewall of the first bit line structure, an air gap is between the inner spacer and an outer spacer, a storage contact between the first and second bit line structures and connected to the drain region, a landing pad structure vertically on the storage contact, and a storage structure vertically on the landing pad structure. The sealing layer seals a top of the first air gap. The sealing layer includes a first sealing layer on a first sidewall of a pad isolation trench, and a second sealing layer on a second sidewall of the pad isolation trench and separated from the first sealing layer.