A quantitative theoretical comparison between two photothermal techniques—the photomodulated reflectance (PMR) and the photothermal infrared radiometry (PTR)—from the standpoint of their relative sensitivity to the thermal and carrier plasma waves in semiconductors is presented. The coefficients representing the relative contributions from the thermal and plasma waves to the total PMR and PTR signals arising as a result of the same temperature increase and photoinjected excess carrier concentration are calculated for three crystalline semiconductors: Si, Ge, and GaAs. The PTR signal is found to be extremely sensitive to the plasma-wave effects exhibiting up to five orders of magnitude higher carrier plasma-to-thermal contrast than that of the PMR method. ©1997 American Institute of Physics.