A chemically amplified negative resist composition comprising an acid generator containing an onium salt having the formula: wherein X 1 and X 2 are each independently methylene, propane-2,2-diyl or ether bond, L is a single bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond, R 1 and R 2 are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, m 1 and m 2 are each independently an integer of 0 to 2, m 3 is 0 or 1, n 1 is an integer satisfying 1 ≤ n 1 ≤ 5+2m 1, n 2 is an integer satisfying 0 ≤ n 2 ≤ 4+2m 2, n 3 is an integer satisfying 0 ≤ n 3 ≤ 8+4m 3, A + is a sulfonium cation having the formula (A-A), an iodonium cation having the formula (A-B), or an ammonium cation having the formula (A-C): wherein R 3A, R 3B, R 3C, R 4A, R 4B, R 5A, R 5B, and R 5C are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, R 5D is hydrogen or a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, any two of R 3A, R 3B and R 3C or any two of R 5A, R 5B, R 5C and R 5D may bond together to form a ring with the sulfur or nitrogen atom to which they are attached, and a base polymer containing a polymer comprising recurring units having the formula: wherein R A is hydrogen, fluorine, methyl or trifluoromethyl, R 11 is each independently halogen, an optionally halogenated C 2 -C 8 acyloxy group, optionally halogenated C 1 -C 6 alkyl group, or optionally halogenated C 1 -C 6 alkoxy group, A 1 is a single bond or C 1 -C 10 alkanediyl group in which an ether bond may intervene in a carbon-carbon bond, t 1 is 0 or 1, x 1 is an integer of 0 to 2, a is an integer satisfying 0 ≤ a ≤ 5+2x 1 -b, and b is an integer of 1 to 3. an acid generator containing an onium salt having the formula: wherein X 1 and X 2 are each independently methylene, propane-2,2-diyl or ether bond, L is a single bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond, R 1 and R 2 are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, m 1 and m 2 are each independently an integer of 0 to 2, m 3 is 0 or 1, n 1 is an integer satisfying 1 ≤ n 1 ≤ 5+2m 1, n 2 is an integer satisfying 0 ≤ n 2 ≤ 4+2m 2, n 3 is an integer satisfying 0 ≤ n 3 ≤ 8+4m 3, A + is a sulfonium cation having the formula (A-A), an iodonium cation having the formula (A-B), or an ammonium cation having the formula (A-C): wherein R 3A, R 3B, R 3C, R 4A, R 4B, R 5A, R 5B, and R 5C are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, R 5D is hydrogen or a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, any two of R 3A, R 3B and R 3C or any two of R 5A, R 5B, R 5C and R 5D may bond together to form a ring with the sulfur or nitrogen atom to which they are attached, and wherein X 1 and X 2 are each independently methylene, propane-2,2-diyl or ether bond, L is a single bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond, R 1 and R 2 are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, m 1 and m 2 are each independently an integer of 0 to 2, m 3 is 0 or 1, n 1 is an integer satisfying 1 ≤ n 1 ≤ 5+2m 1, n 2 is an integer satisfying 0 ≤ n 2 ≤ 4+2m 2, n 3 is an integer satisfying 0 ≤ n 3 ≤ 8+4m 3, A + is a sulfonium cation having the formula (A-A), an iodonium cation having the formula (A-B), or an ammonium cation having the formula (A-C): wherein R 3A, R 3B, R 3C, R 4A, R 4B, R 5A, R 5B, and R 5C are each independently a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, R 5D is hydrogen or a C 1 -C 20 monovalent hydrocarbon group which may contain a heteroatom, any two of R 3A, R 3B and R 3C or any two of R 5A, R 5B, R 5C and R 5D may bond together to form a ring with the sulfur or nitrogen atom to which they are attached, and a base polymer containing a polymer comprising recurring units having the formula: wherein R A is hydrogen, fluorine, methyl or trifluoromethyl, R 11 is each independently halogen, an optionally halogenated C 2 -C 8 acyloxy group, optionally halogenated C 1 -C 6 alkyl group, or optionally halogenated C 1 -C 6 alkoxy group, A 1 is a single bond or C 1 -C 10 alkanediyl group in which an ether bond may intervene in a carbon-carbon bond, t 1 is 0 or 1, x 1 is an integer of 0 to 2, a is an integer satisfying 0 ≤ a ≤ 5+2x 1 -b, and b is an integer of 1 to 3. wherein R A is hydrogen, fluorine, methyl or trifluoromethyl, R 11 is each independently halogen, an optionally halogenated C 2 -C 8 acyloxy group, optionally halogenated C 1 -C 6 alkyl group, or optionally halogenated C 1 -C 6 alkoxy group, A 1 is a single bond or C 1 -C 10 alkanediyl group in which an ether bond may intervene in a carbon-carbon bond, t 1 is 0 or 1, x 1 is an integer of 0 to 2, a is an integer satisfying 0 ≤ a ≤ 5+2x 1 -b, and b is an integer of 1 to 3.