Heteroepitaxial SrO films grown on Si(001) are characterized by reflection high energy electron diffraction and x-ray photoelectron spectroscopy. Special emphasis is put on the interface chemical, structural, and thermal stability because SrO films can be used as template layers for growing crystalline high-k oxides on Si(001). Ultrathin SrO layers of good crystalline quality with sharp interface with Si(001) can be grown at low temperature (50 degrees C) and low partial-oxygen pressure (< 10(-7) Tort). In this case, plastic strain relaxation occurs rapidly at about one-monolayer SrO coverage. At higher temperature (500 degrees C) both strontium,and oxygen react with silicon to form a crystalline silicate with a composition close to Sr2SiO4. This silicate is thermodynamically unstable and, when annealed, transforms into a different silicate close to SrSiO3. (c) 2007 American Vacuum Society.