Epitaxial Ir silicide films were grown on p-Si(100) substrates at 450°C by codeposition of Ir and Si with different Si/Ir atomic ratios. Epitaxial Ir 3 Si 4 was grown on Si(100) as pure Ir was deposited at a substrate temperature of 450°C. The Ir 3 Si 4 /Si(100) interface remained smooth although intermixing occurred during deposition of Ir on Si(100). Ir 3 Si 4 was the phase formed on Si(100) even with higher codeposition ratios, but the Ir 3 Si 4 /Si(100) interface became rougher at higher codeposition ratios. The interface roughness occurring with higher Si/Ir codeposition ratios was attributed to the spatial inhomogeneity of the Si/Ir ratio on a Si(100) surface during the codeposition. The different degrees of intermixing due to the inhomogeneous surface would make the Ir 3 Si 4 /Si(100) interface rough. To obtain a sharp interface, deposition of pure Ir on Si(100) at high temperature is suggested.