A method of fabricating an integrated circuit device includes forming first and second gate patterns on surfaces of a semiconductor substrate in PMOS and NMOS regions, respectively, of the substrate. P-type source/drain regions are epitaxially grown on opposite sides of the first gate pattern in the PMOS region to exert compressive stress on a first channel region therebetween adjacent the first gate pattern. N-type source/drain regions are epitaxially grown on opposite sides of the second gate pattern in the NMOS region to exert tensile stress on a second channel region therebetween adjacent the second gate pattern. Related devices are also discussed.