This paper focuses on the susceptibility to electromagnetic interference (EMI) of chopper operational amplifiers, which are usually preferred to common ones when low-noise and low-offset features are required. The demodulation of EMI carried out by such devices is investigated analyzing the linear distortion that results from the modulation and the demodulation of the signal to be amplified, as well as the nonlinear distortion of the EMI that mostly takes place in the amplifier's input stage. The analysis is extended to feedback chopper amplifiers, and the conclusions drawn are checked performing several measurements on a test chip designed and fabricated to this purpose.