Electron-counting rules were applied to understand the stability, structural preference, and;physical properties of metal disilicides. Following-predictions made: by 14 electron counting rules; the ordered semiconductor ReGaSi, the first ternary phase in this system, was proposed and successfully synthesized. It crystallizes with a primitive tetragonal structure (space group P4/nmm), closely-related to that of MoSi2-type ReSi2, but with Ga and Si orderly distributed in the unit cell. The band structure, density of states, and crystal orbital calculations confirm the electron count hypothesis to predict new stable compounds. 'Calculations, based on 14 electrons per ReGaSi units, show a small indirect band gap of similar to 0:2 eV around Fermi level betWeen full and empty electronic States. Additionally, first-principles calculations confirm the site preference of Ga and Si, which is observed through the structural refinement. Experimental niagnetic measurements verified the predicted' nonmagiktic properties of ReGaSi.