A semiconductor device and a method for forming the same are disclosed. The semiconductor device includes a first junction region formed at the bottom of a vertical pillar, a bit line formed below the first junction region, and an insulation film formed below the bit line. As a result, the 4F2-sized semiconductor device is provided and the bit line is configured in the form of a laminated structure of a conductive layer and a polysilicon layer, so that bit line resistance is reduced. In addition, the semiconductor device reduces ohmic contact resistance by forming silicide between the conductive layer and the polysilicon layer, and includes an insulation film at a position between the semiconductor substrate and the bit line, resulting in reduction of bit line capacitance. Therefore, the sensing margin of the semiconductor device is increased and the data retention time is also increased.