The solid solubilities of aluminum in silicon in the temperature range of 1016-1622 K have been measured by introducing aluminum into solid silicon by passing a molten silicon-aluminum zone through single crystalline silicon with temperature gradient zone melting method. The maximum solubility was found to be 4.3 x 10(-4) in molar fraction around 1450 K. The activity coefficient of aluminum in solid silicon at infinite dilution relative to the pure solid state was determined as RT ln gammaAl(s)(0) = 93200(+/-1000) - 14.5(+/-0.8) T (J/mol) (1016-1622 K). (C) 2003 The Electrochemical Society.