A compact single-shot complementary metal-oxide semiconductor (CMOS) spectral sensor for the visible range (wavelength 400–700 nm) is presented. The sensor consists of two-dimensional silicon nitride-based photonic crystal (PC) slabs atop CMOS photodetectors. The PC slabs are fabricated using one-step lithography and amenable to monolithic integration into CMOS image sensors. Featuring a small footprint of 300μm×350μm, the sensor can successfully measure the spectra over the 400–700 wavelength range with a best resolution of 1 nm. The footprint of the sensor may be further reduced to enable hyperspectral imaging with high spatial resolution.