A metastable silicide phase with a composition of Pt 2 Si 3 has been obtained by using ion-beam mixing techniques. To form the phase, a thin PtSi film on a Si substrate was first converted into a Si-rich amorphous Pt-Si alloy by implantation with energetic ions through the PtSi-Si interface. The amorphous alloy then transformed into the metastable crystalline phase upon post annealing at 350-500°C. X-ray diffraction analysis showed that the Pt 2 Si 3 phase has a hexagonal crystal structure with lattice parameters a=3.841 Å and c=11.924 Å and there are ten atoms per unit cell. The phase was unstable at temperatures above 550°C and transformed back to PtSi and Si. The metastable Pt 2 Si 3 phase was found to exhibit a superconducting transition onset at about 4.2°K and becomes completely superconductive below 3.6°K.