The white light emission phenomenon of the WOx solid state incandescent light emitting device with respect to the annealing temperature has been investigated. Light was emitted after being stressed with a gate voltage above the dielectric breakdown voltage. The emission light intensity increased with the increase of the post deposition annealing temperature. It increased with the magnitude of the stress voltage under the continuous driving condition or the duty cycle number in the pulsed driving scheme. The device emitted lights with high color rendering indices and stable CIE coordinates. The light emission process lasted for more than 1,300 hours continuously in air without failure except the slight change of the optical properties. The above results could be explained with the thermal excitation of the conductive path formed in the dielectric film.