A semiconductor device includes: a substrate having a base and an array of semiconductor pillars extending from the base, the substrate being formed with a plurality of trenches, each of which extends into the base and has two opposing trench side walls; a first insulative liner layer formed on each of the trench side walls of each of the trenches and divided into upper and lower segments by a gap that leaves a bit-forming surface of each of the trench side walls uncovered by the first insulative liner layer; and a plurality of buried bit lines, each of which extends into the base from the bit-forming surface of a respective one of the trench side walls of each of the trenches.