Schottky barrier avalanche photodiodes have been fabricated onn‐type high‐purity epitaxial GaAs. These devices have their largest response at wavelengths beyond the usual absorption edge for high‐purity materials. The absorption mechanism involves the Franz‐Keldysh shift of the absorption edge, and the higher response at the longer wavelengths can be explained by a much higher ionization coefficient for holes than for electrons. The results indicate that the ratio of &bgr;pto &agr;nis even larger than previous measurements have given.