A negative type electron beam sensitive resist film of CMS (chloro-methyl poly-styrene) is developed in a dry environment without using a vacuum system. The resist film is selectively exposed to an electron beam to form a latent image of a desired pattern therein and, then, subjected to irradiation by deep UV having a spectral component of 2537 .ANG. or shorter in an oxidizing gas such as atmospheric air. The average thickness decrease speeds during the dry development are 12 .ANG./min and 300 .ANG./min respectively for the portions exposed and unexposed to the electron beam, revealing a contrast ratio of 100 to 4 in terms of the remaining resist film thickness. A film of PGMA (poly-glycidyl metha-acrylate), and other negative type electron beam sensitive resists, may also be developed by the same method.