A pioneering non-destructive technique has been developed to precisely determine the depth of buried PN junctions in silicon wafers through terahertz (THz) emission spectroscopy. By stimulating charge carriers with ultrafast optical pulses, transient photocurrents near the junction emit broadband THz waves that encode spatial and structural information. Analyzing these signals allows for nanometer-scale mapping of junction positions without wafer damage. This breakthrough could greatly enhance semiconductor manufacturing and quality control, providing rapid, high-resolution metrology crucial for next-generation electronic devices.