The effects of nitrogen on GaAsP light-emitting diodes grown by hydride vapor phase epitaxy are described. Nitrogen acts as an isoelectronic trap and this localized state makes GaAsP a widely used material for from-yellow-to-red visible light-emitting diodes. The photoluminescence and electroluminescence spectra, brightness, and reliability were investigated systematically in line with the function of nitrogen concentration, from 0 (without nitrogen) to 2.3×10 19cm -3. When the nitrogen concentration reached 2.3×10 19cm -3, the total emission in the photoluminescence spectrum at 4.2 K showed a redshift. The study provides clarification of the effects of nitrogen on the diodes and demonstrates that the characteristics of the diodes strongly depend on the nitrogen concentration.