A theoretical analysis is made of nonlinear effects in the propagation of ultrasound in many-valley semiconductors and semimetals. The case of low temperatures, when the interaction of electrons with an acoustic wave is very strong and the lattice absorption is weak, is considered. A characteristic feature is that the deformation electron-phonon interaction shows no dispersion in a wide range of frequencies. This results in a considerable distorition of nf the waveform because of the electron nonlinearity even at low sound intensities. An analysis of this distortion shows that a shock acoustic wave due to the electron nonlinearity may form under certain conditions. The velocity and thickness of the front of this wave and the distance in which it forms are estimated, and its evolution is considered. The estimates obtained demonstrate the possibility of observing such a shock acoustic wave in a real experimental situation.