Scandium oxide (ScOx) thin layers are deposited by high-pressure sputtering (HPS) for physical and electrical characterization. Different substrates are used for comparison of several ScOx/Si interfaces. These substrates are chemical silicon oxide (SiOx), H-terminated silicon surface and silicon nitride (SiNx), obtained by either electron-cyclotron-resonance chemical vapor deposition or plasma enhanced nitridation of the Si surface. Transmission electron microscopy images show that a 1.7 nm thick SiOx layer grows when ScOx is deposited on H-terminated silicon surface. We demonstrate that interfacial SiNx has some advantages over SiOx used in this work: its permittivity is higher and it presents better interface quality. It also avoids Si oxidation. An improvement of one order of magnitude in the minimum of interface trap density is found for SiNx with respect to the SiOx, reaching values below 2×1011 cm−2 eV−1. HPS deposited ScOx films are polycrystalline with no preferential growth direction for the used deposition conditions and their properties do not depend on the substrate. This material could be a candidate for high-k material in flash memory applications.