The activation energy of the shallow donors in n-type CuInSe2 is calculated from the available data of n and μ versus T. The variation of this energy with electron concentration is analyzed taking into account the screening effect of the charge carriers. A critical concentration of ncb = 1.4 × 1017 cm−3 above which the Fermi level merges into the conduction band and another nc = 5.7 × 1017 cm−3 that defines Mott's metal—insulator transition, are estimated. These values, that set the lower and upper limits for metallic and variable range hopping conductions, respectively, seem to agree with reported experimental data.