The slow degradation of single‐heterostructure Ga1−xAlxAs LED’s has been investigated. The samples which show the fast degradation are completely rejected by the selection of DLD‐free LED’s. Selection procedures and the results of accelerated aging tests for over 10 000 h are presented. The activation energy of the slow degradation is found to be 0.57 eV. Extrapolated room‐temperature half‐life in excess of 5×106h is estimated. The degradation coefficients are not affected significantly by the operating current density (3.5–10 kA/cm2).