We report a novel measurement technique for the wide‐band determination of the frequency response of photodetectors. It is based upon the accurate measurement of the photocurrent noise spectra under illumination with a light‐emitting diode. The high sensitivity of −200 dBm/Hz within a frequency regime from 10 MHz to 1.6 GHz renders it particularly attractive for investigating the response behavior at low optical input levels and for characterizing frequency‐dependent gain phenomena. The practical potential of the method is illustrated by applying it to various types of InGaAs‐based photodetectors (p‐i‐nand avalanche photodiodes and metal‐semiconductor‐metal photodetectors).