By using an achiral monomer and a photoinitiator, we introduced polymer networks into the Sm-C* phase of an antiferroelectric liquid crystal that forms ferro-, ferri-, and antiferroelectric phases. We then investigated the temperature dependence of Bragg wavelengths selectively reflected from these samples and found that the reflection bands shift to shorter wavelengths with increasing polymer concentration. The intermediate and the Sm-C*(A) phases dominate over the Sm-C* phase for polymer concentration ≥4% by weight and the Sm-C* phase disappears completely for a 6% polymer sample.