An earlier letter reported microwave (70.2 GHz) measurements of the relative permittivity &egr;rof high‐resistivity GaAs in the temperature range between 100° and 300°K. This letter extends the measurements to 600°K. Over the entire temperature range 100° <T< 600°K, the permittivity is observed to fit the expression &egr;r(T) = &egr;r(0){1 + &agr;T}, where &egr;r(0) = 12.79 ± 0.10 and &agr; = 1.0 × 10−4deg−1.