A semiconductor device employs an asymmetrical buried insulating layer, and a method of fabricating the same. The semiconductor device includes a lower semiconductor substrate. An upper silicon pattern is located on the lower semiconductor substrate. The upper silicon pattern includes a channel region, and a source region and a drain region spaced apart from each other by the channel region. A gate electrode is electrically insulated from the upper silicon pattern and intersects over the channel region. A bit line and a cell capacitor are electrically connected to the source region and the drain region, respectively. A buried insulating layer is interposed between the drain region and the lower semiconductor substrate. The buried insulating layer has an extension portion partially interposed between the channel region and the lower semiconductor substrate.