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.