A temperature-dependent linearity correction function is derived using ground calibration data for the spatial infrared imaging telescope (SPIRIT III) radiometer. First, a small-signal analysis is used to derive linearity correction functions for each array at several focal plane temperatures. These functions are used to derive a single temperaturedependent linearity correction function for each array. The arrays exhibit some detector-dependent nonlinearity. A temperature- and detectordependent linearity correction function is developed by modifying the temperature-dependent array-average linearity correction function so that the half-scale nonlinearity is correct for each detector in the array. Using the nonuniformity correction (NUC) coefficient of variation (COV) as a metric, this temperature- and detector-dependent linearity correction function results in a COV between 0.35 to 2.6% for all arrays, depending on the array and integration mode.