Multiple peaks observed in the temporal evolution of the luminescence of GaAs excited by an ultrashort pulse are attributed to the effect of back-surface reflection. The luminescence components originating from the direct emission and the back-surface reflection are well distinguished using up-conversion luminescence. At an appropriately high excitation energy a sharp peak in the luminescence evolution is observed in a self-assembled InGaAs/GaAs quantum dot sample, which is attributed to stimulated emission excited by the back-surface reflection.