High resolution soft x-ray photoelectron spectroscopy with synchrotron radiation is used to study the interfaces of SiO2/Si(111), SiO2/Si(100), Si(111)/Si3N4, and SiO2/Si3N4 for device-quality ultrathin gate oxides and nitrides. The thin oxides and nitrides were grown by remote plasma deposition at a temperature of 300 degrees C. Aftergrowth samples were further processed by rapid thermal annealing for 30 s at various temperatures from 700 to 950 degrees C. The Si(111)/Si3N4 samples were air exposed and formed a thin similar to 6 Angstrom SiO2 layer with a Si(2p) core-level shift of 3.9 eV, thus allowing us to study both the Si(111)/Si3N4 and SiO2/Si3N4 interfaces with a single type of sample. We obtain band offsets of 4.54+/-0.06 eV for SiO2/Si(111) and 4.35+/-0.06 eV for SiO2/Si(100) with film thicknesses in the range 8-1 Angstrom. The Si(111)/Si3N4 nitrides show 1.78+/-0.09 eV valence-band offset for 15-21 Angstrom films. This value agrees using the additivity relationship with our independent photoemission measurements of the nitride-oxide valence-band offset of 2.66+/-0.14 eV. However, we measure a substantially larger SiO2/Si3N4 Delta E-V value of 3.05 eV for thicker (similar to 60 Angstrom) films, and this indicates substantial differences in core-hole screening for films of different thickness due to additional silicon substrate screening in the thinner (15-21 Angstrom) films.