Provided are a semiconductor device and a method of fabricating the same. The semiconductor device includes: a single electron box including a first quantum dot, a charge storage gate on the first quantum dot, and a first gate electrode on the charge storage gate, the charge storage gate exchanging charges with the first quantum dot, the first gate electrode adjusting electric potential of the first quantum dot; and a single electron transistor including a second quantum dot below the first quantum dot, a source, a drain, and a second gate electrode below the second quantum dot, the second quantum dot being capacitively coupled to the first quantum dot, the source contacting one side of the second quantum dot, the drain contacting the other side facing the one side, the second gate electrode adjusting electric potential of the second quantum dot.