Both the method enabling numerical modeling of fluctuation phenomena in semiconductor devices as well as experimental results of noise current in Hg0.68Cd0.32Te n-on-p photodiodes are presented. While the concept of the applied numerical method was derived earlier [J. Appl. Phys. 90 (3) (2001) 1318], it has been enhanced in this paper by taking into account the influence of temperature fluctuations. The method is based on the assumption that the fluctuations of the generation-recombination processes, carrier mobility, heat generation and heat transfer result in the fluctuations of carrier and ionized impurity concentrations as well as fluctuations of carrier motion and temperature. These, in turn, may be expressed by the fluctuations of electrostatic potential, quasi-Fermi levels and temperature. The fluctuations of the electrostatic potential, quasi-Fermi level fluctuations and temperature fluctuations were calculated by solving the set of "transport equations for fluctuations" in which the fluctuations of generation-recombination processes, heat transfer and mobility act as random source terms. The method was applied to a theoretical analysis of the noise current in n-on-p Hg0.68Cd0.32 photodiodes. The noise spectrum in selected HgCdTe photodiodes is calculated and the contribution of different noise sources is determined. Theoretical results are compared with the experimental data. The planar homojunction devices were formed on LPE grown vacancy doped HgCdTe using a reactive ion etching plasma induced conversion process [J. Electron. Mater. 29 (6) (2000) 841]. (C) 2003 Elsevier Ltd. All rights reserved.