Bismuth oxide films deposited by spray pyrolysis, using bismuth acetate or bismuth chloride, onto clear fused quartz and single crystalline silicon substrates were thermally converted into bismuth silicate compounds. Bismuth silicate compounds' chemical compositions depend on the annealing temperature; Bi2SiO5 is obtained at 600 degrees C and Bi4Si3O12 is produced at 750 degrees C. Forbidden energy optical band gap increases from 3.78 eV for as-deposited films up to 4.89 eV for annealed films. Current densities of 10(-6) A/cm(2), in metal-insulator-semiconductor (MIS) structures, are observed for Bi2SiO5 films at applied electric fields 300 kV/cm and for Bi4Si3O12, films for 2.5 MV/cm. A value of the order of 10.6 was calculated for the apparent dielectric constant of the specimen obtained by annealing at 800 degrees C. (c) 2004 Elsevier B.V. All rights reserved.