A concave micrograting designed for optical communication applications was fabricated by deep x-ray lithography (DXL). The micrograting has a height of 125 μm, a grating pitch of 3 μm, a total of 2584 lines, and a sidewall root-mean-square surface roughness of 5 nm. The designed operational wavelength range is from 1475 to 1625 nm. This micrograting is embedded inside a mirror-planar waveguide to form a spectrometer chip. The Rowland-circle grating mounting scheme is used for the spectral detection. The calculated diffraction efficiency of the third-order diffraction reaches 65% when Au is coated on the grating surface and the blaze angle is suitably chosen. The measured spectral width is 1.1 nm, which is in very good agreement with the calculated result of 0.9 nm. This chip-based grating device can be used as an ultracompact spectrometer or an ultracompact wavelength-division multiplexer in optical communications. Based on this work, our DXL technique can be further developed into an x-ray LIGA method for the mass production of such chip-based spectrometers.