In this paper, we study the noise performance of RTD-gated plasma-wave HEMT THz detectors. It is shown that noise in these devices is dominated by gate tunneling shot noise, and that a smaller effective electron mass promises much improved noise performance by boosting the responsivity while slightly decreasing the noise spectral density (NSD). This implies that it is desirable to realize RTD-gated plasma-wave HEMT THz detectors in material systems with low effective mass. © 2013 IEEE.