PURPOSE: To obtain a positive photoresist having improved heat resistance contg. a photosensitive agent and a crosslinking agent by using a photosensitive crosslinking agent which is not sensitized by the exposure wavelength of the photosensitive agent or using a heat sensitive crosslinking agent which does not cause reaction by the exposure.

CONSTITUTION: Heat resistance of a polymer is enhanced by causing crosslinking of a positive photoresist admixed with a crosslinking agent before or after patterning by treating with heat or light depending on the kind of the crosslinking agent. The treated polymer is subjected to RIE or other treatment. The low mol.wt. components in the positive photoresist are increased in their mol.wt. by the crosslinking agent, and the heat resistance of the product is improved, generating no shear of patterning. The effect is also attained when ion implantation or dry etching is performed. Further, since the crosslinking agent is not sensitized by the light having a wavelength causing a reaction of the photosensitive agent, the function as a photoresist is not at all inhibited.