A method for fabricating a semiconductor device includes: forming an insulation layer over a semiconductor substrate; forming a first conductive layer over the insulation layer; forming a plurality of buried bit lines and insulation layer patterns isolated by a plurality of trenches, wherein the plurality of trenches are formed by etching the first conductive layer and the insulation layer; forming a sacrificial layer to gap-fill the trenches; forming a second conductive layer over the buried bit lines and the sacrificial layer; and forming a plurality of pillars over each of the buried bit lines by etching the second conductive layer.