A semiconductor device includes a buried word line in a substrate and extending along a first direction, a stacked nanowire structure over the buried word line, a first source/drain region and a second source/drain region on opposite sides of the stacked nanowire structure, and a bit line contact and a capacitor contact over the first source/drain region and the second source/drain region, respectively. A method for manufacturing the semiconductor device includes the steps of forming a buried word line extending along a first direction in a substrate, mounting an epitaxy silicon sheet on the substrate and the buried word line, forming a stacked nanowire structure over the buried word line, forming a first source/drain region and a second source/drain region on opposite sides of the stacked nanowire structure, and forming a bit line contact and a capacitor contact over the first source/drain region and the second source/drain region, respectively.