The literature on the activitation of sphalerite for flotation by short-chain xanthates leaves unanswered the question of whether a compact surface film of activator sulfide is necessary or merely sufficient for high flotation recoveries. Studies by guarnaschelli and plaksin indicate that xanthate adsorption and flotation of sphalerite are increased with increasing hole/electron ratio. These results, and the known acceptorlike behavior of many heavy-metal impurities in zinc sulfide, suggest tht activation may result from a traditional semiconductor dopng effect at the surface. Using the theory of chemisorption states on ionic crystals as developed by levine and mark, the Bureau of Mines has carried out a calculation to estimate the surface-state energies of various metals when they are substituted at zinc sites on (110) sphalerite surfaces. Based on a simple madelung-born treatment of ionic solids, the calculation indicates that many of the metals known to activate sphalerite for subsequent flotation have lower surface-state energies than nonactivators. The results of these calculations are discussed from the standpoint of consistency with the proposed activation mechanism and observed flotation results. The satisfactory agreement obtained is taken to be support for the proposed mechanism, and further elaboration of a surface-doping model is attempted.