A novel dry develop method of photoresist - "unzipping development" by flood UV irradiation is described. Evaluated resist consisted of poly-methyl methacrylate (PMMA) and unzipping inhibitors such as p-benzoquinone (p-BQ) and 4,4'-diazide diphenylmethane(4,4'-DDM). As a preliminary experiment has shown that 4,4'-DDM was superior to p-BQ as an unzipping inhibitor, a resist : PMMA added with 40 wt% was mainly evaluated. At patterning exposure (600 ~ 1200 mJ/m2 at 210 ~ 280 nm), 4,4'-DDM in the exposed area fixed into polymer. Then, 4,4'-DDM in the unexposed area was removed in vacuo (0.4 mmHg at 120°C for 1 hr). Finally, negative resist pattern of 1.6 μm was developed by flood UV irradiation (24 J/cm2 at 254 nm) at 90 ~ 130°C without using any solvent. Mechanistic studies were carried out by using IR and UV analyses.