Ferroelectric devices are extremely useful for dynamic random access memories applications because of their high dielectric constant. Using ferroelectric device structure, manufacturing cell capacitance df highly integrated memory device is possible. The small feature size requires anisotropic etching. Since the research of (Ba, Sr)TiO3 thin film etching is:seriously lacking, we Studied the surface reaction of (Ba, Sr)TiO3 thin films by using high. density plasma etching. In this study, (Ba, Sr)TiO3 thin films were etched with Cl-2/Ar gas combination in an inductively coupled plasma. This was done by varying the etching parameters. Such as radio frequency power, direct current bias, and chamber pressure. The maximum etch rate of the BST films was 560 Angstrom/min under Cl-2/(Cl-2+Ar) of 0.2, 600 W/250 V, and 5 mTorr. The selectivity of BST to Pt and SiO2 was 0.52, 0.43, respectively. The surface reaction of the etched (Ba, Sr)TiO3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) using narrow scan spectra. Ba is removed by chemical reaction such as BaCl2 and physical sputtering. Ar ion bombardment is more effective than chemical reaction between Sr and Cl to remove Sr. Ti is removed by chemical reaction such as TiCl4 with ease. The results of secondary ion mass spectrometer analysis;were compared with the results of XPS analysis and the results were the same.