The room‐temperature spectral detectivity of Cr‐doped GaAs has been examined in the impurity excitation region out to 1.7 μ, a range which includes the wavelengths of several important lasers as well as low‐loss optical fibers. The results include values of D∗ greater than 1011 cm Hz1/2/W in the photoconductive mode, and 1010 cm Hz1/2/W in the photomagnetoelectric mode. Small carrier lifetimes, ∼10−8 sec, offer the potential of high‐speed operation; however, the measured response times are much larger, ∼10−3–10−2 sec, because of very high input impedances. Formulas are presented to show the variation of D∗ with relevant parameters, and means of improving the performance are discussed.