Electron spin resonance analysis of (100)Si/LaAlO3 structures reveals the absence of a Si/SiO2-type interface in terms of archetypal Si-dangling bond-type Si/SiO2 interface defects (P-b0,P-b1). With no P-b-type defects observed, this state is found to persist during subsequent annealing (5% O-2+N-2 ambient) up to T-an similar to 800 degrees C, indicating a thermally stable and abrupt Si/LaAlO3 interface. In the range T-an similar to 800-860 degrees C, however, a Si/SiO2-type interface starts forming as evidenced by the appearance of P-b0 defects and, with some delay in T-an, the EX center (a SiO2 associated defect) attesting to significant structural/compositional modification. The peaking of the defect density versus T-an curves indicates that the interlayer with SiOx nature breaks up upon annealing at T-an >= 930 degrees C, possibly related to crystallization and silicate formation. No LaAlO3-specific point defects could be detected. (c) 2006 American Institute of Physics.