Carrier concentration (N) in the channel layers of pseudomorphic In0.5Ga0.5P/In0.2Ga0.8As/GaAs heterostructure field-effect transistors (HFETs) is evaluated by Raman scattering measurements. The coupled mode between the InGaAs longitudinal optical phonons and electrons in the InGaAs channel shifts continuously to a low wave number with an increasing N in the InGaAs channel. Preliminary calculation indicates that N can be determined with an error of less than 0.35×1018/cm3 in the 1018/cm3 order range, which corresponds to a 100 mV HFET threshold voltage. Raman scattering measurement is nondestructive and has a high spatial resolution as small as 1 μm in diameter. Thus, this measurement is promising in HFET wafer selection.