The low temperature (77 K) photoconductivity spectra of CdS crystals are studied at different fre quencies of photoexcitation modulation. The effect of transformation of the photoconductivity spectrum from type I to type II is observed, as modulated photoconductivity excitation is used instead of unmodulated excitation. A model of the fine (excitonic) structure formation in the spectra of the modulated photoconduc tivity excitation for the semiconductor is proposed.