We investigate the nonlinear drift response of electrons in Si, GaAs, and InP crystals to high-power electromagnetic waves by means of a Monte Carlo technique, with the aim of developing an efficient frequency converter for 1 THz output radiation. Drift velocity amplitudes and phases determining the conversion efficiency are calculated for the first, third, and fifth harmonics in the pumping wave amplitude range of 10 < E-1 < 100 kV/cm, for frequencies between 30 and 500 GHz, and at the lattice temperatures of 80, 300, and 400 K. It is found that the efficiency is a maximum at the pumping wave amplitude of the order of 10 kV/cm depending on the intervalley electron scattering parameters and the lattice temperature. Cooling the nonlinear crystal down to the liquid-nitrogen temperature enhances the efficiency several times in Si and by orders of magnitude in GaAs and InP. This is promising for obtaining a 10% conversion efficiency. (C) 1998 American Institute of Physics. [S0021-8979(98)00919-0].