We have synthesized GaAs−GaxIn1-xP (0.34 < x < 0.69) core−shell nanowires by metal−organic vapor phase epitaxy. The nanowire core was grown Au-catalyzed at a low temperature (450 °C) where only little growth takes place on the side facets. The shell was added by growth at a higher temperature (600 °C), where the kinetic hindrance of the side facet growth is overcome. Photoluminescence measurements on individual nanowires at 5 K showed that the emission efficiency increased by 2 to 3 orders of magnitude compared to uncapped samples. Strain effects on the band gap of lattice mismatched core−shell nanowires were studied and confirmed by calculations based on deformation potential theory.