AbstractWhistler‐mode extremely low frequency hiss emissions commonly exist in the plasmasphere and the plasmaspheric plume and contribute to the precipitation loss of the radiation belt electrons. How these hiss waves are generated remains a critical unanswered question. Here we report the large‐amplitude (up to 1.5 nT) hiss waves in the plasmaspheric plumes, nearly an order of magnitude stronger than previous observations. These waves are found to propagate toward higher latitudes, and the corresponding frequency dependence of wave power can be qualitatively (but not quantitatively) explained by the modeled linear instability of hot electrons near the equator. At the high‐frequency end of hiss spectra, the discrete rising tones are shown to emerge, similar to the situation of whistler‐mode chorus in the plasmatrough. These data and modeling suggest that these large‐amplitude hiss waves were generated within the plasmaspheric plume probably through a combination of linear and nonlinear instabilities of hot electrons.