A semiconductor device includes a semiconductor substrate formed with a plurality of trenches, a plurality of trench capacitor type DRAM unit cells including capacitors formed in the trenches and cell transistors formed to be adjacent to the trenches respectively, a plurality of impurity doped regions including boundaries connecting the trenches and the cell transistors and formed in outer peripheries of the trenches, respectively, and a plurality of reverse conduction type impurity regions formed by doping regions of the substrate under the cell transistors with impurity of a reverse conduction type relative to the impurity doped regions, respectively.