A grating-based ultra-compact spectral sensor head was developed to overcome obstacles in characteristics, cost, and size, and it was designed for commercialization in large volume applications. More and more compact spectrometers have been brought to market in recent years—for example, those used for food and beverage quality tests based on measuring sugar content—but their spread is still limited because the conventional types don’t fully fulfill the market requirements. The ultra-compact spectral sensor’s characteristics have been improved while reducing cost and size. Its 20 nm wavelength resolution, equivalent to that of conventional compact spectrometers, was made possible by applying multiplex reflection and small collimation. Using nano-imprint technology, a grating was replicated onto a concave surface inside a compact surface-mount device package. On the opposite side of the concave grating, an entrance slit and a mirror that directs light onto the grating were directly formed on a high-sensitivity CMOS linear image sensor that is sensitive to the 640-1050nm range. The 15μm wide entrance slit was formed on the CMOS silicon chip using MEMS technology, and a short-wavelength cut filter was attached to the entrance window. By reducing the number of components, the structure was simplified. An ultra-compact package measuring 11.7mm × 4mm × 3.05mm and weighing about 0.3g is made possible while maintaining good characteristics and reasonable cost.