Ferroelectric BaTiO3 films with different thicknesses were deposited on "tensile" Si substrates buffered with 100 nm LaNiO3 by radio frequency sputtering. X-ray diffraction measurements demonstrate a high (0 0 1)-orientation and in-plane tensile strain in all BaTiO3 films. With increasing BaTiO3 thickness from 200 to 400 nm, the in-plane lattice constant is decreased and out-of-plane lattice constant increased. High-resolution transmission electron microscopy observations reveal two different in-plane lattice constants in the adjacent twinning domains, thus confirming that the BaTiO3 film is under an in-plane polarization state. The temperature-dependent dielectric measurement results show that the ferroelectric to paraelectric phase transition temperature is enhanced for both BaTiO3 films. However, the enhanced phase transition temperature shows a decrease tendency from 200 to 400 nm BaTiO3, which coincides with the change of lattice constants and can also be interpreted as the result of the internal strain relaxation. (C) 2008 Elsevier B.V. All rights reserved.