lonization during thermal collisions of two identical alkali-metal atoms in the same nP state is studied. In the approximation of the dipole-dipole interatomic interaction, the widths and shifts of autoionizing quasi-molecular states, which describe Auger transitions to electronic levels nearest in energy (near-threshold decays) of a quasi-molecular ion, are calculated. The influence of an interaction of close configurations 2nP and nS, (n +1)S on the ionization process is considered. Partial cross sections of ionization to a specific near-threshold state are calculated. The ionization cross section is found to undergo oscillations as the principal quantum number n varies, and the cause for this phenomenon is elucidated. The region of the applicability of the results obtained is established.