It is well-known that quantitative analysis of major elements by SIMS is generally difficult because of the matrix effect. In the present paper we examined some basic problems of the major element analysis of Cd_xHg_1-xTe (CMT) which is known to be easily damaged by various kinds of beams. It was shown that the matrix effect in quantification can be reduced by detecting postionized monoatomic ions for O₂⁺ and Ar⁺ primary beams. In the case of Cs⁺ bombardment, detection of the cationized molecular ions, which are formed via one kind of post-ionization process, also proved to be effective. In all the cases, good linear relationships between the secondary ion intensity and the primary ion current density were obtained in the log-log plot. The intensity decrease of Hg⁺, however, was observed along with depth profiling of the bulk sample. This phenomenon was correlated with the morphological changes caused by ion irradiation.