We report the numerical calculation of Ar 9+ · · · Ar 13+ , Kr 13+ · · · Kr 17+ , and Xe 19+ · · · Xe 23+ ion yield in the laser field with intensity exceeding 10 19 W/cm 2 . The results of the calculations agree with the experimental data [K. Yamakawa et al., Phys. Rev. A 68, 065403 (2003)] (for the Ar ions) or qualitatively (for the Kr ions). The theoretical results disagree with the experimental data for the Xe ions. We discuss the possible influence of the relativistic effects on this disagreement between theory and experiment. We obtained the approximation formula for the position of the maximum ionic population with the given ionization multiplicity Z depending on the radiation intensity. This position is described by the power function of Z; the exponent is determined by the dependence of sequential ionization potentials on Z value. We discuss the dependence of the approximation formula parameters on the value of the FWHM of the laser pulse.