A method of fabricating a semiconductor device includes preparing a substrate including a first region and a second region, sequentially forming a first semiconductor layer and a second semiconductor layer on the first and second regions, patterning the first and second semiconductor layers to form a lower semiconductor pattern and an upper semiconductor pattern on each of the first and second regions, selectively removing the lower semiconductor pattern on the second region to form a gap region, and forming gate electrodes at the first and second regions, respectively.