The temperature dependence of the via hole etch rate is reported for argon/chlorine plasma etching of indium phosphide in an electron cyclotron resonance etcher. The indium phosphide via hole etch rate was first established for several wafer chuck temperatures. Then the temperature of the wafer was estimated by measuring the heating effect of the plasma and the cooling effect of the helium backside cooling. The wafer temperature was then substituted for the wafer chuck temperature. The etch rate as a function of wafer temperature was found to exist in two regimes. The first regime is where the vapor pressure of the etch by product gas (indium chloride) is below the etcher chamber pressure. In this first regime the activation energy was calculated to be 0.45 +/- 0.05 eV. The second regime is where the vapor pressure of the etch by product gas (indium chloride) is above the etcher chamber pressure. In the second regime the activation energy was calculated to be 0.06 +/- 0.03 eV.