This paper reviews recent advances in emission of THz radiation from our original dual-grating gate high-electron mobility transistors (HEMT's) originated from two-dimensional plasmons. The dual grating gates can alternately modulate the 2D electron densities to periodically distribute the plasmonic cavities along the channel, acting as an antenna. The sample was fabricated with standard GaAs-based heterostructure material systems, succeeding in emission of broadband (0.5 to 6.5 THz) radiation even at room temperature from self-oscillating 2D plasmons under appropreate DC-bias conditions. Currently maximum available THz output power is estimated to be on the order of 1 to 10 μW from a single die active area of 75 × 75 μm2 with an excellent power conversion efficiency of 10-3. The fabricated device was introduced to the Fourier-transform infrared spectroscopy as a microchip THz source. Water-vapor absorption spectrum was successfully observed at 300 K, which is proven to the standard data provided by NASA.