We report optical reflectivity measurements on Ba1-xKBiO3 (x = 0, 0. 15) single crystals in the frequency range 70-30 000 cm(-1) and at different temperatures in an attempt to understand the transport mechanism in the semiconducting state before it undergoes semiconductor-metal transition. For x = 0. 15, at 400 K, we find a hump in reflectivity at approximate to 1280 cm(-1). N-eff of total IR transition shifts towards low frequency as temperature increases above 300 K. We suggest the presence of new and thermally excited states in the Peierls band gap and the possible new IR excitations. (C) 2003 Elsevier Science B.V. All rights reserved.