A method of manufacturing a p-channel MOS transistor including forming a structure by subsequently stacking gate insulating layer pattern and a gate conductive layer pattern on a semiconductor substrate. The method also includes forming first offset spacer layers on sides of the gate conductive layer pattern, forming a second-offset-spacer-layer insulating layer to cover the semiconductor substrate, the first offset spacer layer, and the gate conductive layer pattern, implanting p-type impurity ions in the second-offset-spacer-layer insulating layer by performing a first ion implanting process, and forming a second offset spacer layer and a gate spacer layer on the first offset spacer layer by performing a spacer layer forming process. The method further includes forming source/drain extension regions by diffusing the implanted p-type impurity ions by performing a thermal treatment process, and forming source/drain regions passing through the respective source/drain extension regions by performing a second ion implanting process by using the gate spacer layer as an ion implanting barrier.