An n-type MOSFET (NMOS) is implemented on a substrate having an epitaxial layer of strained silicon formed on a layer of silicon germanium. The MOSFET includes first halo regions formed in the strained silicon layer that extent toward the channel region beyond the ends of shallow source and drain extensions. Second halo regions formed in the underlying silicon germanium layer extend toward the channel region beyond the ends of the shallow source and drain extensions and extend deeper into the silicon germanium layer than the shallow source and drain extensions. The p-type dopant of the first and second halo regions slows the high rate of diffusion of the n-type dopant of the shallow source and drain extensions through the silicon germanium toward the channel region. By counteracting the increased diffusion rate of the n-type dopant in this manner, the shallow source and drain extension profiles are maintained and the risk of degradation by short channel effects is reduced.