The semiconductor CdS is widely used as a window material in many photovoltaic applications. The interface between CdS and the front collector transparent conducting material plays a pivotal role in the solar cells; a physical understanding and control of the interface morphology are needed in order to improve the device performance. Cadmium stannate has recently been recognized as an important transparent conducting material in light of its superior physical properties over the conventional transparent conducting oxides. Physical understanding of the interface between CdS and cadmium stannate is therefore pf great practical interest. For this study, the grazing incidence x-ray scattering (GIXS) technique has been demonstrated very useful for the nondestructive characterization of the interface morphology in a variety of layered structures, thus, it is well suited for this task. In the present work, various thin films of CdS deposited on cadmium stannate are investigated by the GIXS technique using synchrotron radiation. Also, similar measurements were made with CdS films deposited on glass substrates for comparison. Variations of surface and interfacial roughness as well as lateral correlation lengths of interface height fluctuations as functions of film thickness and processing conditions are investigated.