A series of CVD-grown 3C-SiC/Si(100) films of different growth times, and hence film thicknesses, are studied by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). XPS showed that the surfaces of the samples consist of Si oxides (SiO2 and SiOx where x < 2) and unreacted C.H. Unreacted elemental Si is also present and its amount decreases with increasing growth time. This surface overlayer is further investigated by changing the photoelectron take-off angle and from chemical etching studies. Compositional variations of the SiC films are also studied using SIMS.