A device includes a substrate having a first side and a second side, a first transistor that includes a first gate over a first protrusion and a first source region and a first drain region interposing the first protrusion, a first buried contact disposed adjacent to the first protrusion and having at least a portion extending into the substrate, a first contact plug disposed over the first drain region, first conductive lines disposed over the first contact plug and electrically connecting to the first drain region by the first contact plug, first via penetrating through the substrate and connecting the first buried contact; and second conductive lines disposed over the second side of the substrate and electrically connecting to the first via. The first buried contact is electrically connecting to the first source region or the first gate.