Surface-enhanced Raman scattering (SERS) is a technique that can deliver label-free, real-time, and multiplex detection of target molecules. However, the development of this potential tool has been impeded by an obstacle: reliability. Because SERS detection relies on the very localized (< 10 nm) hot spot, severe intensity fluctuation occurs as the molecule thermally diffuses in and out of the tiny spot, making it difficult to quantify the information of analytes. Here, we address the problem by greatly expanding the effective area of a hot spot. The breakthrough is realized by a few layers of conformally nanostructured InGaN, which introduce wafer-scale charge coupling at the molecule/metal/semiconductor interface. These additional coupling channels interconnect plasmonic nanojunctions, rendering the SERS-active surface spreading over 1200 μm2 in Raman mapping. The result allows us to capture trace molecules with increased chances and stabilized signals, paving a way for SERS to enter real-life applications.