A new process for low-frequency (300 kHz) pulse plasma etching of GaAs and mask materials (Au, Cu, and Ni) using a mixture of ClCH3 and H-2 in the pressure range of 40-80 mTorr is reported. The ion-bombardment r(i) and chemical component r(c) of the etch rate are deconvolved by measuring the GaAs etch rate as a function of pulse width, duty cycle, pressure, and etch time constant t1/2. The etch rate is modeled using a phenomenological rate equation with fitting parameters : t1/2, r(i), and r(c).