High‐energy electrons (≈7 MeV) were used to radiation dope extrinsic silicon. Bothn‐ andp‐type silicon photodetectors were fabricated using this doping technique. The 500°K blackbody responsivity, spectral response, and peak detectivity were determined for these devices. The peak detectivity values measured were 4.8×1011cm Hz1/2W−1at 2.15 &mgr; for 0.1‐&OHgr; cmn‐type devices and 3.7×1011cm Hz1/2W−1at 40 &mgr; for 10‐&OHgr; cmp‐type detectors. A comparison of the thermally generated background majority carrier concentration for radiation‐doped and conventional impurity‐doped detectors is made.