Rather high temperature raise of internally oxidized Ag-Sn alloy contact materials due to a high contact resistance inherent to such materials, is eliminated. The high contact resistance which is caused by high concentration or supersaturation of metal oxides including tin oxides about contact surfaces, is avoided by having solute metals sublimated, reduced or extracted about the contact surface before the internal oxidation thereof. Sublimation and other treatments may be made after having the materials subjected to internal oxidation.