In terms of the phenomenological Kittel's model the electron effect on the physical properties of the crystals in the region of transitions from the antiferroelectric to the paraelectric and ferroelectric phases is considered. In the absence of an external electric field the electron subsystem affects the properties of both the antiferroelectrics-semiconductors and the ferroelectrics-semiconductors in a substantially identical way, provided that the macroscopic screening processes are disregarded. In external fields, the effect of the excited electron concentration on the properties of ferroelectric and antiferroelectric crystals is described with the aid of various expressions. The theoretical results obtained are in qualitative agreement with the effects revealed experimentally in photosensitive antiferroelectrics.