The dependence of the reflection coefficient at contradirectional four-wave mixing in the photorefractive semiconductor GaAs on its spatial orientation is theoretically investigated. The coupled waves equations were used for the calculations, in the derivation of which it was assumed that secondary mixed holographic gratings with a phase-amplitude structure are formed in the crystal. The theoretical model took into account the combined contribution of the linear electro-optical, photoelastic, and inverse piezoelectric effects, as well as the natural absorption of the recording medium. It was found that when using the GaAs semiconductor, the maximum diffraction efficiency at contradirectional four-wave mixing is achieved in the case when the normal to the cut plane of the crystal is oriented along one of the < 234> directions. In the case when the normal to the cut plane is directed along < 112> and < 111>, the reflection coefficient can reach 90% and 80% of the maximum possible value, respectively. Keywords: Four-wave mixing, phase-conjugation front, photorefractive crystal, reflection coefficient, coupled wave equations.