The impact ionization process in the ⟨100⟩, ⟨110⟩, and ⟨111⟩ crystallographic directions in InP has been investigated by analysis of photomultiplication and multiplication noise data from InP avalanche photodiodes. This is the first report of such measurements for (110)‐oriented InP and the first consistent investigation of impact ionization in the three principal crystallographic directions. Our measurements indicate that, unlike the reports for GaAs, no significant orientation dependence of the impact ionization coefficients exists in InP. Momentum‐randomizing collisions with phonons, which result in intervalley transfer of energetic electrons, are believed to be the reason for the lack of anisotropy in the electron impact ionization coefficients.