Three-dimensional semiconductor device with air gap

According to the disclosure, highly integrated memory cells and a semiconductor device having the same are provided. According to an embodiment, a semiconductor device comprises a plurality of memory cells vertically stacked on a base substrate, each of the plurality of memory cells includes, a bit line vertically oriented from the base substrate, a capacitor horizontally spaced apart from the bit line, an active layer horizontally oriented between the bit line and the capacitor, a word line positioned on at least one of a top surface and bottom surface of the active layer and horizontally extending in a direction crossing the active layer, and a capping layer positioned between the word line and the bit line and including, at least, a low-k material and an air gap.