An improved method for the determining of the small-signal model parameters has been demonstrated and successfully applied to E-up InGaAlAs/GaAsSb/InP double heterojunction bipolar transistor (DHBT). The adopted model takes into account the distributed nature of base resistance and base/collector capacitance. The proposed method can alleviate some difficulties encountered among conventional extracting techniques, namely the use of additional test structures, forward-biased measurements at specific conditions, and empirical optimization process. The method is based on analytical approach with only two approximations dividing the frequency range in three parts (low, middle. and high frequency range). An extraction technique for extrinsic and intrinsic base/collector capacitances using S-parameters data is also presented in this paper. An excellent agreement between measured and simulated S-parameters in the frequency range of 40 MHz-50 GHz is obtained over a wide range of bias points. (C) 2009 Elsevier Ltd. All rights reserved.