<p>This study presents a methodology for extracting the lateral distribution of electrical defect concentration (<i>N</i>_B) associated with gate-insulator traps contributing to low-frequency noise (LFN) of self-aligned top-gate (SA TG) coplanar indium–gallium–zinc oxide (IGZO) thin-film transistors (TFTs) using low-frequency noise (LFN) analysis. The proposed approach utilizes modulation of the effective channel length by drain voltage (or source voltage) together with an LFN power spectral density model to obtain the average defect concentration corresponding to different effective channel lengths, from which the lateral defect distribution can be derived. The extracted results reveal that pristine devices exhibit a relatively uniform defect distribution along the channel with slightly higher values near the source and drain regions. After the application of saturation stress, a noticeable increase in the defect concentration is observed near the drain side of the channel, indicating localized degradation of the gate insulator. These findings demonstrate that LFN analysis can be used to experimentally probe the spatial distribution of gate-insulator defects in SA TG coplanar IGZO TFTs, providing a useful diagnostic approach for studying reliability degradation mechanisms in advanced display backplane devices.</p>