SiCl4/SF6 GaAs/AlGaAs selective dry etching by a pulse-excited inductively coupled plasma source with operating pressure lower than 1.0 Pa was investigated. With 10 kHz and 50% duty ratio pulsed excitation, GaAs/AlGaAs etching selectivity was doubled (>200) compared to continuous wave (cw) operation, in which the selectivity was not adequate enough (similar to 100) to use for device fabrication. With pulsed excitation, we speculate that the electron temperature and [Cl]/[F] radical density ratio decrease. Pulse parameters such as the duration of the ''on'' and ''off'' periods and the duty ratio dependence are also investigated, showing that the selectivity was determined by the duty ratio of the pulse. The advantage of pulse excitation over conventional cw excitation is clearly shown.