Reactive ion etching process for InP using BCl3/O2/Ar high density inductively coupled plasma was investigated. The experimental design method proposed by the Taguchi was utilized to cover the whole parameter range while maintaining reasonable number of actual experiments. Results showed that the ICP power and the chamber pressure were the two dominant parameters affectsing etch results. It was also observed that the etch rate decreased and the surface roughness improved as the ICP power and the bias voltage increased and as the chamber pressure decreased. The Addition of oxygen to the gas mixture drastically improved surface roughness by suppressing the formation of the surface reaction product. The optimum condition was ICP power 600W, bias voltage -100V, 10% $O_2$, 6mTorr, and $180^{circ}C$, resulting in about 0.15$mu extrm{m}$ etch rate with smooth surfaces and vertical mesa sidewalls Also, the maximum etch rate of abut 4.5 $mu extrm{m}$/min was obtained at the condition of ICP power 800W, bias voltage -150V, 15% $O_2$, 8mTorr and $160^{circ}C$.