The response surface methodology (RSM) has been used in this study to investigate the effect of various control factors on the performance of silicon trench etch in high-density transformer coupled plasma (TCP) on Cl2/HBr/O2-based chemistry. The TCP source power, bias power, and Cl2 content of the Cl2/HBr mixture were the process variables. The etch rate and sidewall profile angle were employed as the response items for RSM analysis. Quantitative relationships between etching characteristics and process parameters have been established. The possible mechanisms are also proposed to explain the different sidewall profile angles as varying the parameters.