Epitaxial iron-nickel alloy silicide has been successfully grown on (111) Si for the first time using a new method of chemically electroless plating of Fe-Ni thin films on Si with subsequent annealing schemes. The deposited film was found to be amorphous by analytical scanning transmission electron microscopy. The alloy silicide phase formed during two-step vacuum annealing and was found to have an epitaxial relationship with the substrate Si. The composition of the eptaxial alloy silicide was identified by an energy dispersive analysis for x rays in the electron microscope. A small amount of nickel was found in the alloy silicide. The crystal structure of the silicide phase was analyzed to be that of an orthorhombic phase of FeSi2. The orientation relationships of the silicide phase with respect to the substrate were identified to be (033̄) (Fe,Ni)Si2∥(022̄) Si, (055) (Fe,Ni)Si2∥(4̄22) Si, and [100] (Fe,Ni)Si2∥[111] Si. Typical arrays of regular interfacial dislocations of edge type, 1000 Å in spacing, were found throughout the epitaxial regions. The formation and some potential applications of the epitaxial Fe-Ni alloy silicide are discussed.