A semiconductor device includes a bit line structure located on a semiconductor substrate, an outer bit line spacer located on a first side surface of the bit line structure, an inner bit line spacer including a first part located between the bit line structure and the outer bit line spacer and a second part located between the semiconductor substrate and the outer bit line spacer, and a block bit line spacer located between the outer bit line spacer and the second part of the inner bit line spacer. A first air-gap is defined by the outer bit line spacer, the inner bit line spacer, and the block bit line spacer.