We report the growth of (001)- and (111)-oriented (Ba,Sr)TiO3 (BST) films on Pt/TiOx/SiO2/Si substrates by RF magnetron sputtering without buffer layers. Interestingly, it was observed that the crystallographic orientation of prepared films strongly depended on O-2/(Ar+O-2) mixed ratios (OMR) during deposition. The samples with OMR=0% showed a perfect (001) orientation, while those with OMR ranging from 10% to 50% showed a preferential (111) orientation. The perfectly (111)-oriented BST film deposited with OMR=30% exhibited a broader grain size distribution than the (001) textured BST film. At +/- 400 kV/cm, high tunability of 52% and 68% can be achieved for (001)- and (111)-oriented BST films, respectively.