A method of fabricating a semiconductor device includes forming a conductive layer on a semiconductor substrate, forming an insulating layer on the conductive layer, forming a word line and isolation trenches by patterning the insulating layer and the conductive layer, forming an isolation layer that fills the isolation trenches, forming a cell contact hole in the insulating layer such that the cell contact hole is self-aligned with the word line and exposes the word line, and forming a cell diode in the cell contact hole.