Semiconductor devices having plug insulators

Provided are a semiconductor device and a method of fabricating the same. The semiconductor device includes a first bit line structure extending in a first direction, a second bit line structure extending in the first direction and spaced apart from the first bit line structure, a storage contact plug located between the first bit line structure and the second bit line structure, and extending in a second direction perpendicular to the first direction, a first plug insulator located between the first bit line structure and the second bit line structure, and configured to contact a side surface extending in the second direction of the storage contact plug, and a plug isolation pattern located between the first bit line structure and the first plug insulator.