Neutron rocking curves of Si 111 channel-cut crystals were measured in the (+, -) parallel setting of double crystal arrangement. They showed discrepancies from the usual dynamical diffraction theory at the tail parts. It was found that extra scattering appearing close to the Bragg peak is explained in the frame work of the dynamical theory if reflections of neutrons at back surfaces are taken into consideration. Crystal designs to reduce such reflections are described.