Abstract: Disclosed is a method for forming micro-patterns on base plates such as for semiconductor integrated circuits, particularly by development, wherein a radiation sensitive negative resist film is formed on the base plate and irradiated according to pattern designs, and the non-irradiated portions of the film is dissolved by a liquid developer comprising a mixture of a good solvent selected from the group of alkyl esters of acetic acid, having an alkyl group containing 1 to 5 carbon atoms, and a poor solvent selected from the group consisting of alicyclic compounds and alkyl ethers of ethyleneglycol having an alkyl group containing 1 to 5 carbon atoms. The method can minimize swelling of irradiated portions of the resist film and can accelerate dissolution of non-irradiated portions of the resist film, so that desired micro-patterns with excellent edge shape quality can be obtained.