Covalent inhibitors offer powerful therapeutic advantages but require comprehensive profiling to define their on- and off-target activities. Here, we apply two stability-based proteomic methods, SPROX and TPP, to characterize protein targets of the KRASG12C inhibitor ARS-1620 in H358 cell lysate. Both methods identified ligand-induced protein stability shifts, collectively recovering the known on-target KRAS as well as multiple off-targets. Comparative analyses with ABPP and pull-down datasets highlighted ALDH1A3 as a reproducible off-target. Bottom-up proteomics mapped Cys314 as the major ARS-1620 modification site on ALDH1A3, and enzymatic assays confirmed dose-dependent inhibition. Covalent docking supported a favorable binding pose within the retinal-binding pocket. Together, these findings demonstrate that stability-based proteomics provides an effective, derivatization-free strategy for covalent drug target identification.