A semiconductor device includes a substrate and a memory structure disposed over the substrate. The memory structure includes a pair of first conductive lines, a channel element disposed between the pair of the first conductive lines and formed with an air gap therein, a first memory element disposed to separate one of the pair of the first conductive lines from the channel element, and a second memory element disposed to separate the other one of the pair of the first conductive lines from the channel element. A method for manufacturing the semiconductor device is also disclosed.