A positive working, aqueous base developable photosensitive polybenzoxazole (PBO) precursor composition based on a partially trimethylsilyl (TMS) protected PBO precursor and a bisphenol A based 1,2-naphthoquinone diazide-4-sulfonate (DNQ-4) photosensitive compound has been developed. The polymer was prepared from a low temperature polymerization of 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BisAPAF) and isophthaloyl chloride (IC), followed by reacting with trimethylchlorosilane. Subsequently, thermal cyclization of the PBO precursor at 350 degreesC produced the corresponding thermally stable PBO. The inherent viscosity of the precursor polymer was 0.35 dl/g. The cyclized PBO showed a glass transition temperature (T-g) at 309 degreesC and a 5% weight loss at 550 degreesC in nitrogen. The structure of the precursor polymer and the fully cyclized polymer were characterized by FTIR and H-1 NMR. The photosensitive PBO precursor containing 20 wt% DNQ-4 photosensitive compound showed a sensitivity of 172 mJ/cm(2) and a contrast of 1.33 in a 3-mum film with a 0.6 wt% tetramethylammonium hydroxide (TMAH) developer. A pattern with a resolution of 5 mum was obtained from this composition. The novel PBO precursor photosensitive composition showed a significant improvement in dark film loss after development and could be used to make a thick film resist.