Surface segregation and interaction effects of In and Sb in (GaIn)As/Ga(AsSb)/(GaIn)As- “W”-type quantum well heterostructures (“W”-QWHs) are investigated by high angle annular dark field scanning transmission electron microscopy with atomic resolution. “W”-QWHs are promising candidates for type-II laser applications in telecommunications. In this study, independent (GaIn)As and Ga(AsSb) quantum wells as well as complete “W”-QWHs are grown by metal organic vapour phase epitaxy on GaAs substrate. The composition is determined with atomic resolution by comparison of the experimental data to complementary contrast simulations. From concentration profiles, an altered segregation in “W”-QWHs in comparison to single (GaIn)As and Ga(AsSb) quantum wells grown on GaAs is detected. In and Sb are clearly influencing each other during the growth, including blocking effects of In incorporation by Sb and vice versa. Especially, growth rate and total amount of Sb incorporated into Ga(AsSb) are decreased by In being present.