A semiconductor device includes a base structure comprising a semiconductor substrate, a first conductive structure disposed on the base structure, and extending in a first direction, the first conductive structure including lower layers, and at least one among the lower layers including carbon, and a data storage pattern disposed on the first conductive structure. The semiconductor device further includes an intermediate conductive pattern disposed on the data storage pattern, and including intermediate layers, at least one among the intermediate layers including carbon, a switching pattern disposed on the intermediate conductive pattern, and a switching upper electrode pattern disposed on the switching pattern, and including carbon. The semiconductor device further includes a second conductive structure disposed on the switching upper electrode pattern, and extending in a second direction intersecting the first direction, and a hole spacer disposed on a side surface of the data storage pattern.