The ion emission of the ‘impurity-matrix’ type from the semiconductor materials of GaN; GaP; GaAs and GaSb, doped by carbon and oxygen, was studied. The CAMECA IMS 4f and IMS 7f SIMS instruments (CAMECA SAS, France) were used. It was shown that the most stable molecular ions of the ‘impurity-matrix’ type have outer electron shell filled so that a complete octet is formed (including the charge). Such ions are able to overcome the distance from the target to ion detector without decay. Ion current intensities of each matrix are normalized to the current intensity of the carbon or oxygen mono-impurity. The results show that the highest intensity is exhibited by ion currents of dimers whose electron shells (including the negative charge) make a complete octet. We assume that the formation of dimers is the evidence of chemical nature of the impurity-matrix interaction. Probably, this reaction is induced by bombarding with primary ions. Copyright © 2012 John Wiley & Sons, Ltd.