A MEMS spectrometer includes an optical substrate having a first face and a second face. A first semiconductor substrate is attached to the first face and includes a slit for passing incident light to the optical substrate, at least one integrated reflective grating, and at least one integrated detector array. A second semiconductor substrate is attached to the second face of the optical substrate and includes at least a first integrated mirror and a second integrated mirror. The first integrated mirror is positioned to receive the incident light transmitted by the optical substrate and to provide reflected light, and the integrated reflective grating, second integrated mirror and integrated detector array are positioned so that they are optically coupled to one another by the optical substrate to process the reflected light.