We consider the ultrafast kinetics of evolution of optical phonons in a photoinjected highly excited plasma in semiconductors. The state of the nonequilibrium ('hot') phonon system is described in terms of the concept of a nonequilibrium temperature, referred to as quasitemperature, per mode, which can be experimentally characterized and measured. The phonon emission time shows that optical phonons are preferentially produced, well in excess of equilibrium, in a reduced off-center region of the Brillouin zone. The phonons in this region are responsible for the phenomenon referred to as 'hot-phonon temperature overshoot.' Most of the phonons, namely, those outside such a region, are only weakly to moderately excited, and mutual thermalization of the nonequilibrium carriers and optical phonons follows, typically, in the tenfold picosecond scale. All these results are influenced by the experimental conditions, which we discuss on the basis of calculations specialized for GaAs. Comparison with experimental data is presented.54161131111316