The intensities of x‐ray transitions in highly charged ions in the Bei, Bi, and Neiisoelectronic sequences have been calculated as functions of electron density. The intensities of the transitions from the 2sn2pm3pconfiguration, relative to the intensities from the 2sn2pm3sand 2snpm3dconfigurations, are strong functions of electron density in high‐density plasmas. The density sensitivity occurs at electron densities between 1016cm−3(for Si ions) and 1022cm−3(for Kr ions). Opacity is unimportant for plasma dimensions that are characteristic of dense laser‐produced plasmas. These x‐ray line ratios represent a promising new density diagnostic for high‐density plasmas.