Abstract The optical absorption spectra of Zn 1− x Mn x Se single crystals are investigated, for x = 0.05, 0.06, 0.15, 0.30, 0.45, and 0.50. The measurements were taken from 28 K to RT in the wavelength range between 390 to 520 nm. Four well‐resolved bands below the fundamental absorption edge are observed corresponding to internal transitions from the ground to the excited state within the Mn ion. An initial decrease of the energy gap with the concentration x for all temperatures is found. A break in the monotonic dependence of the energy gap with temperature is observed at high Mn concentrations and low temperatures. This anomalous behavior is associated with the s–d and p–d exchange interactions occurring in diluted magnetic semiconductors (DMS).