This paper presents results of numerical studies of the influence of plasma waves in semiconductor samples on their photoacoustic and piezoelectric photothermal spectra. This influence was examined theoretically with the newly derived compact model describing the spatial distribution of the instantaneous temperature field in the semiconductor samples in the presence of plasma waves. This model enabled computations of the photoacoustic and piezoelectric spectra in the front and rear experimental configurations and determination of the influence of plasma waves on them.