Interactions of PtTi, NiTi, AlPt, and AlNi compounds with Si substrates were analyzed by a combination of backscattering spectrometry and transmission electron microscopy. The reaction occurs via the migration of Si into the alloy matrix at temperatures between 500 and 600 °C. Uniform mixing rather than phase separation is observed in all the systems investigated. Ternary compounds (PtTiSi, NiTiSi2, AlPtSi, and Al2Ni2Si) are formed in the reacted layer and exhibit a high stability to heat treatment at elevated temperatures. These reactions were rationalized in terms of the free energy change of the reacted systems and the mobilities of various atoms.