The general principles and design theory ofp‐njunction detectors with narrow spectral responses are described. These detectors do not require the use of external filters and are capable of maintaining their narrow spectral response over large fields of view. Use of zinc diffusion inn‐type gallium arsenide has produced detectors peaking in the neighborhood of 8850 Å with characteristic bandwidths on the order of 200 Å and quantum efficiencies from 0.2–0.3 electrons per photon. The principle has been experimentally extended to a second material, indium‐arsenide—phosphide, whose composition is tuned to provide a narrow spectral response peaking at 1.06 &mgr;. The experimental results are compared with theoretical predictions.