Temperature dependence of sharp photoluminescence and absorption peaks, which originate from then=1 free heavy‐hole exciton, in a ZnSe–ZnS strained‐layer superlattice (Lb=50 Å andLw=25 Å) with a multiple quantum‐well structure has been investigated. A dominant mechanism responsible for broadening in the excitonic linewidth below 85 K is an ionized donor impurity scattering of free excitons that occurs in addition to the acoustic phonon scattering. On the other hand, it is suggested that the linewidth of the excitonic absorption peaks at high temperature is attributed to the scattering of free excitons withLOphonons. Stark shifts and a concomitant quenching in intensity of the exciton line were observed under electric fields.