Marker experiments have been used to study the formation and the oxidation of two semiconducting silicides with large band gaps. Both Ru2Si3 and Ir3Si5 have been shown to form by mechanisms dominated by the motion of the silicon atoms. The same is true for the growth of SiO2 over these two silicides under conditions which ensure the integrity of the silicide layers. IrSi has also been shown to grow mostly through the motion of silicon. © 1987.