With increasing uncertainties in the modeling and processing of semiconductor devices, it is essential that the sources of failures be identified once the devices are manufactured. In this paper, we present a methodology to diagnose the problems in broad-band amplifiers by determining the most important small signal parameters of the internal transistors. We use an evolutionary algorithm specifically designed to mimic the expected errors to ensure fast convergence to the correct solution. Sensitivity analysis is used to determine the set of the most impactful small signal parameters and to guide the evolutionary search. Experimental results indicate the proposed algorithm determines the parameters accurately and it scales well in terms of accuracy and computation time. ©2004 IEEE.