A chemical amplification type resist composition contains as a photoacid generator a sulfonyldiazomethane compound of the formula (1): wherein R1 is C1-10 alkyl or C6-14 aryl, R2 is C1-6 alkyl, G is SO2 or CO, R3 is C1-10 alkyl or C6-14 aryl, p is an integer of 0 to 4, q is an integer of 1 to 5, 1≦p+q≦5, n is 1 or 2, m is 0 or 1, and n+m=2. The composition is suited for microfabrication, especially by deep UV lithography because of many advantages including improved resolution, minimized line width variation or shape degradation even on long-term PED, minimized debris after coating, development and peeling, and improved pattern profile after development.