An improved copper base alloy having excellent thermal resistance and electric conductivity. The alloy consists essentially of from 0.0005 to 0.01 percent boron, a material selected from the group consisting of phosphorus from 0.001 to 0.01 percent, indium from 0.002 to 0.03 percent, tellurium from 0.001 to 0.06 percent and mixtures thereof, and the balance copper and inevitable impurities. The copper base alloy may further contain from 0.002 to 0.05 percent magnesium whereby the magnesium imparts further enhanced thermal resistance to the alloy.