Disclosed herein is a method for manufacturing a semiconductor device that includes forming a gate pattern on a substrate having a stacked structure including a lower silicon layer, an insulating layer, and an upper silicon layer. The method further includes forming spacers on sidewalls of the gate pattern. Still further, the method includes etching the upper silicon layer using the gate pattern as a mask to form a floating body and expose a portion of the insulating layer. The method further includes depositing a conductive layer over the gate pattern and exposed insulating layer, and performing a thermal process on the conductive layer to form a source/drain region in the floating body.