In0.25Ga0.75As/GaAs quantum dots grown by metalorganic vapor-phase epitaxy in a GaP matrix have been investigated on the atomic scale using cross-sectional scanning tunneling microscopy. The quantum dots have a truncated pyramidal shape with a reversed cone stoichiometry profile. All deposited indium is found within the quantum dots and the occasionally observed quantum rings, while the wetting layer has a GaAsP composition without any indium inside. This indicates an intense lateral material transfer during growth.