AbstractThe thermodynamics of multicomponent plasmas is investigated using a theoretical description where the free energy as a function of density and temperature is the basic quantity. The correlation contribution to the free energy and the chemical potential as well as the excess pressure (exchange plus correlation) are calculated at arbitrary degeneracy by summation over the complex Matsubara frequencies. With increasing degeneracy the numerical effort may be reduced with the help of the large wave‐number approximation or plasmon—pole expressions for the dielectric function. The temperature dependent self‐energy is calculated in the same way. Numerical results are given for the electron system, a hydrogen plasma, and for the electron—hole plasma in highly excited semicon