The yield point phenomenon observed in nanoindentation of metallic single crystals has been attributed to dislocation nucleation. The event is preceded by elastic reversible indentation followed by a rapid increase of indenter tip displacement. A similar event has been seen in epitaxial Co films on GaAs substrates. As these films are on the order of 10 nm thick, the substrate plays a significant role in dislocation behavior as dislocations are emitted at the nucleation site. Epitaxial Fe films 23 and 100 Å in thickness have been grown on GaAs and GaAs with a Sc0.3Er0.7As interlayer. Nanoindentation experiments have been performed using the Hysitron Triboscope, an add-on device to an atomic force microscope. The influence of film thickness, epitaxial interlayer, and biaxial misfit stress on the yield point behavior in the overlayer will be considered.