A grating spectrometer integrated monolithically in the InGaAsP system with a photodiode array for a dense WDM system is presented for the 1.5 μm wavelength region. The chip provides more than 30 wavelength channels with a spacing of 4 nm, a channel crosstalk of approximately −15 dB, an internal photodiode efficiency of 90% and a photodiode capacitance of 0.33 pF. The chip needs no optical adjustments. It is therefore well suited to mass production.