A sharp photoluminescence spectral feature has been observed in ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As-GaAs multiple-quantum-well structures under high-intensity, resonant excitation at the ground-state exciton energy. This feature, which appears below the exciton ground state, emerges from a cold dense system of excitons, but prior to the breakup of excitons into an electron-hole plasma. A collective excitonic state is speculated.