A photoresist‐film thickness measurement method based on absorbance measurement is described. In this case, a 1‐&mgr;m‐thick photoresist film is coated on transparent glass, e.g., a Color Picture Tube panel having a 10–12‐mm thickness and a spherical, rough surface. To measure the absorbance, which corresponds to photoresist‐film thickness, the developed method employs a two‐dimensional scan of a 2‐mm‐diam light beam spot having two wavelengths, 365 nm (measuring wavelength) and 546 nm (reference). By switching wavelengths alternately at 25 Hz, total absorbance of the photoresist film and glass is measured with a ‘‘Dynode feedback’’ circuit system, but only the film thickness is displayed through simple signal processing. As experimental results, a minimum detectable thickness change of 0.001 &mgr;m (resolution) was obtained. The only remaining thing to be considered for practical use is a zero‐level discrepancy, due to different panel lots, for which the value was approximately equal to a 0.1‐&mgr;m thickness change.