We have developed a technique for fabricating polycrystalline thin films of CdS onz‐cut LiNbO3. A single film will show a light‐to‐dark–conductivity ratio of approximately unity with very high sheet resistance after curing. To make a good photoconductor, a second film is then deposited. This film is protected during the subsequent curing from out‐diffusion from the LiNbO3by the first film and develops a light‐to‐dark–conductivity ratio of 10 000 in room light with a sheet conductivity of 10−10s/&laplac; mcd. Films produced by this layered process also possess a remarkably large conductivity‐modulation dependence (20&percent;) on the square of an impressed electric field provided by a traveling surface acoustic wave in the LiNbO3substrate.