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wherein R 100 , R 200 , and R $^{300 }$are as defined above, x- is an anion of any one of the general formulae (5) to (8): 

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wherein R: 1 \ R:11’1, R:11’ 2 , R’c1, R’c 2 , and R’c3 are each independently fluorine or a straight C$_{1 }$-C$_{40 }$or branched 35 or cyclic C$_{3}$-C$_{40 }$monovalent hydrocarbon group which may be substituted with or separated by a heteroatom, R:11’ 1 and R:11’ 2 , or R’c1 and R’c 2 may bond together to 40 form a ring with the segments to which they are attached, R’d is a straight C$_{1 }$-C$_{40 }$or branched or cyclic C$_{3}$-C$_{40 }$ monovalent hydrocarbon group which may be substituted with or separated by a heteroatom. 

5. The resist composition of claim 2, further comprising a nonionic nitrogen-containing compound. 

6. The resist composition of claim 2, further comprising a surfactant which is insoluble or substantially insoluble in water and soluble in alkaline developer and/or a surfactant which is insoluble or substantially insoluble in water and alkaline developer. 

7. A pattern forming process comprising the steps of applying the resist composition of claim 2 onto a substrate, prebaking to form a resist film, exposing the resist film to KrF excimer laser, ArF excimer laser, EB or EUV through a photomask, baking, and developing the exposed resist film in a developer. 

8. The pattern forming process of claim 7 wherein the exposing step is by immersion lithography wherein a liquid having a refractive index of at least 1.0 is interposed between the resist film and a projection lens. 

9. The pattern forming process of claim 8, further com› prising the step of forming a protective film on the resist film, and in the immersion lithography, the liquid is inter› posed between the protective film and the projection lens. 

10. The onium salt compound of claim 1 wherein R$^{44 }$and R$^{55 }$bond together to form a ring with the nitrogen atom to which they are attached, and the ring may have an oxygen atom, sulfur atom or NH moiety interposed therein. 

11. The onium salt compound of claim 10 wherein the ring is selected from the group consisting of the following structures: 

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* * * * * 

