We show that an electron beam passing through a collisionless plasma of “cold” ions and “hot” Boltzmann electrons can give rise to the propagation of supersonic ion-acoustic rarefaction shock waves. These waves are analogous to those predicted by Zeldovich ( Zh. Eksp. Teor. Fiz., 16 (1946) 363) in gas dynamics and complementary to the ion-acoustic compression shock waves in the collisionless plasma described by Sagdeev ( Rev. Plasma Phys., 4 (1966) 23).