Disclosed is a novel negative-working radiation-sensitive resist composition useful in the photolithographic patterning works of resist layers on substrate surfaces in the manufacture of semiconductor devices and capable of giving a finely patterned resist layer with high resolution and having an excellently orthogonal cross sectional profile of the line-wise patterned resist layer with an outstandingly high sensitivity to various actinic rays. The composition comprises, as the essential ingredients, (a) an alkali-soluble resin such as a cresol novolac resin, (b) a specific alkoxymethylated amino resin, e.g., methoxymethylated melamine resin, and (c) a specific triazine compound in a limited weight proportion.