Large reversible variations in carrier concentration, Hall mobility, and carrier lifetime have been produced in indium arsenide by heat treatment. For material cut from the parent ingot, carrier lifetimes measured by the photoelectromagnetic‐photoconductive ratio method increase by a factor of over 20 as a result of slow cooling from 850°C. Heat treatment at temperatures of 450°C and above increases the carrier concentration ofn‐type material and decreases the carrier concentration ofp‐type material. Such variations are reversed by heat treatment at temperatures below 350°C. In this way, changes in the carrier concentration of over 1017cm−3have been produced, and InAs has been converted fromptontype. Various heat treatment mechanisms are examined. It is shown that the experimental results are consistent with the model proposed by Kurtz and Kulin involving the segregation and dispersion of donor impurities to and from dislocations.