A semiconductor device and a method for fabricating the same are disclosed, in which floating body effect is reduced by applying a bias to a body in an SOI MOSFET. The semiconductor device includes first and second impurity ion implanting layers of a conductivity type formed in a semiconductor substrate having a buried oxide film and surface silicon layers thereon, first and second transistors of a conductivity type respectively formed on the first and second impurity ion implanting layers, having source/drain regions and a gate, trenches formed between the first and second transistors, single crystal silicon layers connected to any one of the source/drain regions of the respective transistors and the first and second impurity ion implanting layers at sides of the trenches, and carrier exhausting electrodes connected to the first and second impurity ion implanting layers at one sides of the respective transistors, for exhausting carrier generated by ionization impact in the respective transistors.