Abstract A new mechanism for the charge carrier self-trapping in antiferromagnetic semiconductors is discussed. A charge carrier becomes localized inside a microregion of another AFM phase which is normally unstable but in which the charge carrier energy is lower than in the normally stable AFM phase. An additional gain in the energy is obtained by canting of moments of sublittices inside the localization region. In degenerate semiconductors the afmon pairing is possible with biafmons being stable in a wide range of the charge carrier densities. At larger densities the separation of two AFM phases may occur with formation of many-electron regions of the normally unstable phase. At a certain density this phase transforms from the multiply-connected to the singly-connected with a sharp rise in the conductivity. A possible relation of the afmon pairing and phase separation to HTSC is discussed.