Laser-assisted etching of (100) n-doped GaAs in a Cl-2/Ar atmosphere performed with a pulsed ArF excimer laser (lambda=193 nm, tau=17 ns) was investigated as a function of laser fluence, process thermodynamical parameters (pressure, temperature, and gas phase composition), and carrier concentration. The etching process is shown to result from a combination of photochemically and thermally activated reaction steps. Etch reaction kinetics were found to be 3/2 order in Cl-2 at pressures below 7X10(-3) Torr with an activation energy of 7.8 kcal/mol, attributable to the formation of GaCl3 via the reaction between chemisorbed GaCl2 and Cl radicals from the gas phase. The influence of the etching parameters on surface morphology was also examined. Mirror-like morphologies were achieved using laser fluences below 25 mJ/cm(2), substrate temperatures between 100 and 200 degrees C, and concentrations of Cl-2 in Ar below 2%.