This study examined the effect of applied electric field annealing on the microstructure and microwave properties of Ba0.5Sr0.5TiO3 ( BST) thin films grown on LaAlO3 substrates. The ultraviolet-visible transmission spectra and micro-Raman spectra of these BST thin films revealed the band-gap and lattice vibration to be strongly dependent on annealing with an applied electric field. Based on the structural analyses and microwave properties, the variation in the band-gap, the chemical binding states, and the tunability of the films were attributed to the combined effects of applied electric field annealing in highly elongated BST thin films. (C) 2011 Elsevier B.V. All rights reserved.