Multiplication and noise measurements on InSb avalanche photodiodes have been made from 77° to 125°K. For the diodes studied, the electron ionization rate is much larger than the hole ionization rate and depends only weakly on the field for fields between 5×103and 104V/cm. The electron ionization rate increases and the breakdown voltage decreases with increasing temperature. The dependence of the ionization rate on field and temperature is explained by the weak dependence of the distribution function on field for high fields. The noise measurements are consistent with McIntyre's theory providing that the electron ionization rate is much greater than the hole ionization rate. A current‐controlled negative resistance is observed in InSb avalanche diodes at breakdown.