Thin films of Ba0.5Sr0.5TiO3 (BST) have been deposited by off-axis sputtering on high temperature annealed (1 0 0) MgO substrates. The MgO substrates were annealed in air for 5 h each at different temperatures in the range of 950-1280degreesC, Steps on the MgO surface were first observed for annealing temperatures at 1000degreesC. Additionally, outgrowths from the surface were observed which contributed to the measured rms surface roughness. The maximum step height and rms surface roughness occurred in the vicinity of 1140degreesC. The BST films were deposited at 550degreesC on the annealed MgO substrates and post annealed in oxygen at 780degreesC for 8 h. X-ray diffractometry showed the BST grain structure to be predominantly (1 1 0) and the lattice parameter relatively independent on the MgO annealing temperature. The grain size observed from atomic force microscopy was 100-150 nm. The relative dielectric constant and timing increased in magnitude for BST deposited on MgO annealed at or above 1145degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.