This study investigates GaAs dry etching in capacitively coupled BCl3/N2 plasma at a low vacuum pressure (>100 mTorr). The applied etch process parameters were a RIE chuck power ranging from 100~200 W on the electrodes and a N2 composition ranging from 0~100 % in BCl3/N2 plasma mixtures. After the etch process, the etch rates, RMS roughness and etch selectivity of the GaAs over a photoresist was investigated. Surface profilometry and field emission-scanning electron microscopy were used to analyze the etch characteristics of the GaAs substrate. It was found that the highest etch rate of GaAs was 0.4 μm/min at a 20 % N2 composition in BCl3/N2 (i.e., 16 sccm BCl3 / 4 sccm N2). It was also noted that the etch rate of GaAs was 0.22 μm/min at 20 sccm BCl3 (100 % BCl3). Therefore, there was a clear catalytic effect of N2 during the BCl3/N2 plasma etching process. The RMS roughness of GaAs after etching was very low (~3 nm) when the percentage of N2 was 20 %. However, the surface roughness became rougher with higher percentages of N2.