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State-filling spectroscopy is used to study the effects of alloy intermixing in quantum-dot (QD) ensembles having well-defined electronic shells. Rapid thermal annealing is performed on samples of self-assembled QDs grown with different intersublevel energy spacings. For InAs/GaAs QDs, the intersublevel is tuned between ∼90 and 25 meV. The intense and sharp shell structures observed in photoluminescence indicate unambiguously that the QDs retained their zero-dimensional density of states after the diffusion of the potential, which also causes strong blueshifts (up to ∼200 meV) and a pronounced narrowing of the inhomogeneously broadened emission (down to ∼12 meV).