The acoustic field inside a surface acoustic wave device was studied by means of double‐crystal x‐ray diffraction. Angular satellites in the diffraction pattern were observed due to the coherent scattering on the acoustic superlattice. Satellite dynamics allows determination of the acoustic wave amplitude. Due to the sensitivity of x‐ray diffraction to the direction of atomic displacements, the amplitude of different polarization components in the Rayleigh wave can be obtained.