The authors studied the dry-etching process by chlorine-based inductively coupled plasma for fabricating GaAs suspended photonic crystal cavities. To achieve low optical loss in such resonators, the photonic crystal holes must demonstrate simultaneously smooth sidewalls and good verticality. The influence of various parameters of the inductively coupled plasma process was investigated: a systematic analysis is provided on the dependency of hole sidewall roughness and shape on the process parameters such as gas mixture, etching power, pressure, and rf bias. The authors show that a combination of high pressure, high bias, and high etching power in an inductively coupled plasma with a Cl-2/N-2 chemistry is beneficial for achieving straight and smooth sidewalls, and wall tilt of less than 4 degrees was obtained.