High dielectric constant (K) materials are needed as capacitor insulators in dynamic random access memories and as gate dielectrics in future silicon devices. Band offsets must be over 1 eV for both electrons and holes for low leakage currents. We have calculated the band offsets using the method of charge neutrality levels. Ta2O5 and BST have small conduction band offsets on Si. La2O3, Y2O3, ZrO2, Al2O2 and ZrSiO4 have offsets over 1.5 eV for both electrons and holes, making them better gate dielectrics. Zirconates are better than titanates as they have wider gaps.