We contend that residential segregation should be an essential component of the analyses of socio-ethnic income gaps. Focusing on the contemporary White/African gap in South Africa, we complete Mincer wage equations with an Isolation index that reflects the level of segregation in the local area where individuals dwell. We decompose the income gap distribution into detailed composition and structure components. Segregation is found to be the main contributor of the structure effect, ahead of education and experience, and to make a sizable contribution to the composition effect. Moreover, segregation is found to be harmful at the bottom of the African income distribution, notably in relation to local informal job-search networks, while it is beneficial at the top of the White income distribution. Specific subpopulations are identified that suffer and benefit most from segregation, including for the former, little educated workers in agriculture and mining, often female, confined in their personal networks. Finally, minimum wage policies are found likely to attenuate most segregation’s noxious mechanisms, while a variety of policy lessons are drawn from the decomposition analysis by distinguishing not only compositional from structural effects, but also distinct group-specific social positions.