We report gas-source molecular beam epitaxy of Ga1-xInxNyP1-y grown on GaAs (100) substrates. Bulk Ga1-xInxNyP1-y samples were characterized by high-resolution X-ray rocking curve and photoluminescence (PL). With nitrogen incorporation, the PL peak red-shifts, indicating bandgap reduction. The PL peak energy exhibits an inverted S-shape dependence with temperature, and the low-temperature PL spectra exhibit an asymmetric line shape with a low-energy tail. Both indicate the presence of localized states which dominate the radiative recombination processes at low temperature. Rapid thermal annealing at 700degreesC for 10s in a 100% N-2 ambient improves the Ga0.44In0.56N0.01P0.99 PL intensity by a factor of 10, reduces the line width to two-fifth, and removes the localized states. (C) 2002 Elsevier Science B.V. All rights reserved.