PURPOSE: To enable a fine resist image to be formed without swelling by incorporating dimethylformamide in a developing soln. for a resist made of a polymer contg. a specified trioxabicyclo compd. as structural units.

CONSTITUTION: The developing soln. of a resist contg. as structural units a trioxabicyclo compd. represented by the formula, R being alkyl, incorporates dimethylformamide. This solvent perfectly dissolves the unexposed parts of the resist without leaving the residue, and moreover, it causes extremely small swelling during the development. The swelling can be more suppressed by using a mixture of a poor solvent, such as propylene glycol, with such a soln., thus permitting a resist image good in resolution to be formed and used for semiconductor integrated circuits, etc.