The phase conjugate wave has been obtained by degenerated four-wave mixing (DFWM) with silicon single crystal as the nonlinear medium using Q-switched Nd:YAG lasers. The reflectivity of the phase conjugate mirror (PCM) has been calculated from the theory of the light induced electron-hole-pair density, which produced a phase grating. Experimentally, a reflectivity of 125% of the PCM was obtained and the property of the compensation of the phase aberrations was demonstrated.