A method for fabricating a semiconductor device includes etching a substrate to form a plurality of bodies isolated by a first trench, forming a buried bit line gap-filling a portion of the first trench, etching the top portions of the bodies to form a plurality of pillars isolated by a plurality of second trenches extending across the first trench, forming a passivation layer gap-filling a portion of the second trenches, forming an isolation layer that divides each of the second trenches into isolation trenches over the passivation layer, and filling a portion of the isolation trenches to form a buried word line extending in a direction crossing over the buried bit line.