The impacts of base-to-emitter spacer thickness on the unity gain frequency (f(T)), base resistance (r(B)), base collector capacitance (C-BC) and maximum oscillation frequency (f(max)) of a bipolar junction transistor (BJT) are studied. Using the extracted Y-parameters from a simulated device with structural parameters calibrated to an actual process, the resulting f(T) and f(max) with different spacer thickness is reported. A tradeoff between peak f(T) and f(max) is observed and the process window to obtain high F-T and f(max) is proposed. (C) 2005 Elsevier Ltd. All rights reserved.