Abstract: This paper experimentally investigates the effect of DC bias voltage on the convolution efficiencies of air-gap coupled acoustoelectric convolvers which are made of various surface-treated silicon strips. For the silicon strips which are thermally oxidized to form 1000 Å thick SiO₂ films and then annealed in nitrogen atmosphere, there appear some new phenomena. We have derived their theoretical explanations, but these are here only briefly mentioned.