Calculations have been made to determine the influence of a dense plasma of hot electrons and holes on the primary channels of energy relaxation and redistribution of photoexcited carriers in Si, particularly collisions between carriers, plasmon emission, impact ionization, phonon emission, and carrier diffusion. At high carrier densities, Auger recombination is sufficiently fast to ensure that the electrons and holes rapidly reach quasiequilibrium with a common quasi-Fermi level at a temperature which is lowered by the partitioning of energy into thermally excited plasmons. The appropriate dielectric function has been calculated. At sufficiently high temperatures and carrier densities, energy can diffuse at a rate that is comparable to (and, in some cases, faster than) the rate at which the energy is transferred to the lattice. The steady-state carrier density and temperature, and consequently the ultimate extent to which the lattice is heated, depend critically on the parameters of the exciting laser. © 1980 The American Physical Society.