We report on an experimental study of the nonlinear interaction of Bleustein‐Gulyaev surface waves in photoconducting CdS. The two oppositely travelling surface waves at frequencyf=43 MHz are first amplified and then interact under a semitransparent diffused electrode. The acoustic convolution product is observed at 86 MHz. The level of the detected signal is 36 dB below the two input ones with an interacting length of only 2 mm. There is clear evidence that this nonlinear interaction results from electron phonon scattering; we give the expression for the second‐order potential.