Self-assembled GaInP quantum dots embedded in a Gap matrix were prepared by low-pressure metalorganic vapor-phase epitaxy using the Stranski-Krastanow growth mode. We present photoluminescence (PL) and atomic force microscopy studies of the formation process of three-dimensional quantum sized islands out of a two-dimensional GaInP quantum film. Up to 4 x 10(9) cm(-2) coherently strained quantum islands were formed, emitting at 1.91 eV with a full-width at half-maximum of 38 meV (4 K). The dependence of the optical properties of the quantum dots on growth temperature and composition of the GaInP layer suggests, that the PL behavior is mainly influenced by the growth parameters of GaInP deposition, whereas the structure of the quantum islands and the nominal composition of the GaxIn1-xP layer play only a minor role. These observations and temperature-dependent PL measurements indicate that the coherently strained quantum islands include regions with partially ordered GaInP domains. Operating under optimized growth conditions, we obtained a bright and narrow PL from the quantum dots up to room temperature. The observed strong PL at 1.87 eV (300 K) qualifies self-assembled GaInP quantum islands on GaP for applications in the visible part of the spectrum.