The mechanism of overhang formation in a diazide/novolak photoresist film by the chlorobenzene soak process for lift‐off stencil fabrication is investigated by gel permeation chromatography. The experimental results show that overhang profile formation is controlled mainly by the removal of photoactive compounds (PAC’s) from a resist film. The amount of PAC loss within the modified region in a resist film must be precisely controlled to form a desired overhang profile. The amount of PAC loss depends mainly upon the molecular weight of the PAC’s and the kind of soaking solvent used.