In this article, the degradation of 234 nm AlGaN-based far-UVC light-emitting diodes (LEDs) under constant current stress is studied in-depth by the combination of optical and electrical characterization with an in situ testing method. In addition, the relationship between the degradation and the variation of defects is established by deep-level transient spectroscopy (DLTS) testing. In combination with the capacitance–voltage characteristics, it is found that the significant degradation of optical power is mainly related to the transition of hole trap “

${h}_{{1}}$

” with the energy level of Ev + (0.201–0.243 eV) to “

${h}_{{2}}$

” with the energy level of Ev + 0.624 eV in the active region. The transition is described as the separation of Mg from Mg

$_{\mathbf {Ga}}$

to generate the VGa and combined with other defects to form the VGa-related complex defects. These complex defects as non-radiative recombination centers could contribute to the reduction of injection efficiency and directly lead to the reduction of optical power. On the n-side, the increased concentration of electron trap “

${e}_{{2}}$

” indicates that the crystal quality of material deteriorates further. The leakage current rises slightly, which is primarily due to the increase in the concentration of hole trap “

${h}_{{3}}$

” with deeper energy levels. This study about the defects behavior of 234 nm LED may provide a reference for the fabrication of AlGaN far-UVC LED with higher reliability.

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