High brightness GaP green LED's have been developed by optimizing growth conditions to obtain a high quality p-n junction. In particular, the n-type GaP layer near the junction is greatly lowered in carrier concentration in order to decrease the nonradiative recombination center. The carrier concentration in the n-type GaP layer is decreased to 5-6 × 10 15 /cm 3 near the p-n junction and a minority-carrier lifetime of 800 ns (measured through the EL decay time) is obtained. The best device has a quantum efficiency of 0.45 percent at 12.5 A/cm^{2} with encapsulation. Excellent high-brightness LED lamps of 400 m Cd at a driving current of 20 mA can be obtained by using the high efficiency GaP green LED's.