We developed optical emission spectroscopy based end-point detection techniques for GaAs-based etching in inductively coupled BCl3/Ni-2 plasmas, It was found that an emission peak of Ga (417 run) was quite useful as a tracer for in situ process monitoring during both AlGaAs/GaAs and InGaP/GaAs, multilayer etching. The intensity of the Ga emission peak increased significantly during AlGaAs/GaAs etching in a BCl3/N-2 inductively coupled plasma when the GaAs layer was exposed to the plasma. We found the same result with InGaP/GaAs etching. Utilization of the Ga peak signal is very important during the plasma process for GaAs-based device fabrication, especially for high electron mobility transistors and heterojunction bipolar transistors in order to minimize overetch time during the nonselective etching. The technique provides a breakthrough for in situ end-point detection of GaAs-based nonselective plasma etching.