Preparation of single crystals of LaCuOS, that is a transparent p-type semiconductor exhibiting violet-light emission, was demonstrated by the flux method using NaCl+KCl(1:1) as flux. The crystals were grown in an alumina tube inserted in an evacuated silica glass tube using the starting materials of LazO(2)S and Cu2S, as well as the flux and a small amount of K2S that reduces the coloration of crystals. Transparent colorless laminate crystals were obtained under the optimized crystal growth conditions; growth temperature 850 degrees C, growth time of 72 h and cooling rate 10 degrees Ch(-1). The size of the largest colorless crystal was 3.0 x 2.8 x 0.049 mm(3). The crystal showed transmission as high as 60% and p-type electrical conductivity of 7.1 x 10(-4) S cm(-1) at room temperature. (C) 2008 Elsevier B.V. All rights reserved.