A negative-type photosensitive polyamic acid (PAA) was synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride and 2-(methacryloyloxy)ethyl 3,5-diaminobenzoate in N-methyl-2-pyrrolidinone. Glycidyl methacrylate was added into the PAA solution to yield a photosensitive PAA ester (PAE) by the ring-opening esterification reaction of the carboxylic acid group in the PAA and glycidyl methacrylate. Esterification reactions were conducted with varying reaction temperatures and times. The typical PAE (PAE-C3) with a degree of esterification of 20% was used for a photosensitivity study. We investigated the effects of the postexposure baking temperature, amount of photoinitiator, and exposure dose on the photosensitivity of PAE-C3. Furthermore, a photolithography evaluation was conducted on PAE-C3 in the presence of 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime)-1,2-octanedione as a photoinitiator using a mercury lamp at a 365-nm wavelength. The resolution of the film with 2.0-mu m thickness was about 8 mu m. PAE-C3 cured at 250 degrees C for 60 min was stable up to around 310 degrees C in a nitrogen atmosphere. (c) 2006 Wiley Periodicals, Inc.