The influence of composition variations on crystal structure, differential thermo‐e.m.f., and electronic structure parameters of the alloys CeM2−xSi2+x with M = Fe, Co, Ni, Cu is investigated. It is established that the range of possible mutual atom substitution of 3d elements and silicon increases with the growth of atomic number of the transition element: CeFe2−xSi2+x is a compound with rather narrow homogeneity range (x ≈ 0), CeNi2−xSi2+x and CeCu2−xSi2+x are compounds of variable composition with lattice parameters and electronic structure depending on Ni(Cu) and Si content.