A single-substrate-processing CVD apparatus is used for forming a BST thin film on a semiconductor wafer while supplying a first process gas containing a mixture of Ba(thd).sub.2 and Sr(thd).sub.2, and a second process gas containing Ti(O-iPr)(thd).sub.2 or Ti(thd).sub.2. Precursors of Ba and Sr have lower activation energies and higher resistivities than precursors of Ti. The first and second process gases are supplied from a shower head which has a group of first spouting holes for spouting the first process gas and a group of second spouting holes for spouting the second process gas. The group of the second spouting holes are designed to have diameters gradually decreasing in radial directions outward from the center of a shower region, such that the second process gas is supplied at a spouting rate gradually decreasing in radial directions outward from the center.