A positive-working photosensitive polyimide precursor based on polyisoimide (PII) and 2,3,4-tris(1-oxo-2-diazonaphthoquinone-4-sulfonyloxy) benzophenone (D4SB) as a photoreactive compound has been developed. The polyisoimide was prepared by the ring-opening polyaddition reaction of 4,4’-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA) and 3,3’-diaminodiphenylsulfone (3,3’-DDS), followed by treatment with trifluoroacetic anhydride-triethylamine in N-methyl-2-pyrrolidone (NMP). The polyisoimide film showed excellent transparency to u.v. light, and good solubility in a wide range of organic solvents. The dissolution behaviour of the polyisoimide film containing 20 wt% of D4SB after exposure and post-exposure bake (FEB) has been studied and it has been found that the dissolution rate of an exposed area was similar to 80 times faster than that of an unexposed area, due to the photochemical reaction of D4SB in the polymer film. The photosensitive polyimide precursor containing 20 wt% of D4SB showed a sensitivity of 250 mJ cm(-2) and a contrast of 2.4 with 435 nm light, when it was post-baked at 150 degrees C for 10 min, followed by developing with 5% tetramethylammonium hydroxide solution at 45 degrees C.