It is found that the operating lives of Zn-diffused GaAs electroluminescent diodes depend principally upon the donor concentration. Diodes produced from wafers having 1-2×1018 donors/cm3 have longer operating lives than diodes produced from wafers having 1-2×10 17 donors/cm3. To a lesser extent, operating lives depend upon the Zn-diffusion cycle. Optimum results are obtained by carrying out the diffusion at 750°C for four hours followed at 850°C for 45 min. Apparently there is little or no dependence of operating life upon the donor type (Sn or Si), the crystalline orientation of the wafers, or upon epoxy potting of the wafers. Under continuous operation, light output decreases 5%-10% during the first few hours, and then remains approximately constant thereafter (the maximum test duration was 22 500 h). These diffused diodes are relatively simple to fabricate, have efficiencies of the order of 1% and room temperature risetimes of about 10 nsec. © 1970 The American Institute of Physics.