Abstract This study fills the gap of upper-level energies and the ionization limits of the following configurations: 1s3s1S0, 1s2p3Po0, 1s2p 1Po1, 1s3p1Po1, 1s4p 1Po1, 1s5p1Po1, 1s6p1Po1, 1s2p3Po1, 1s3s3S1, 1s4s3S1, 1s3d 1D2, 1s3d3D2, 1s5d3D2, 1s2p3Po2, 1s3d3D3, 1s4d3D3, 1s5d3D3 in P-XIV and in Cl-XVI currently not listed at NIST. Therefore, in this work the ionization limits with and without relativistic effects are computed for the Helium-like iso-spectrum levels series for the mentioned configurations, for Z = 2 - 17. A total of 254 ionization limits are computed and compared with the available data at National Institute of Standard and Technology. The yield limits departing from NIST ones by not more than 0.00001 eV.