The recombination dynamics of GaAs multiple quantum wells as a function of barrier widthsLBare studied in a semiconductor in the range betweenLB=0.87 nm (superlattice) andLB=18.1 nm (uncoupled wells) by means of cathodo‐ and photoluminescence. With decreasingLBthe nonradiative recombination rate is found to be drastically enhanced, where‐as the radiative recombination probability decreases. Thus a pronounced decrease of the quantum efficiency results. The controlled variation of the barrier width is found to be decisive for an unambiguous identification of the origin of the traps which are responsible for the nonradiative processes: Comparison with a theoretical calculation shows that they are localized at the heterointerfaces andnotin the barriers.