The first measurement of the impact ionization rates for electrons and holes in Al0.48In0.52As is reported. Photomultiplication measurements in pin avalanche photodiodes give &agr;/&bgr;≊2.5–3.0 in the electric field range 3.3×105V/cm≤F≤4.3×105V/cm. This material can therefore be used to implement a potentially high‐performance, long‐wavelength avalanche photodiode, with separate absorption and multiplication regions and a high‐low electric field profile (HI‐LO SAM APD).