The phase transition in K(NO3)(1-x)(ClO3). bulk samples and thick films has been investigated from the dielectric polarisation and temperature dependence of the electrical resistivity. The bulk samples were found to be ferroelectric even at room temperature with an average spontaneous polarisation of 6.72 mu C cm(-2). The spontaneous polarisation increased slightly with increasing chlorate concentration up to x = 0.08. The transition temperature of KNO3 bulk samples was found to be 146 degrees C. The transition temperature of the thick films was found to shift to higher values with increasing chlorate ion concentration. The substitution of the nitrate ions with increasing chlorate ions could lead to the formation of Schottky barriers at the grain boundaries with a resultant space charge, which could set up space charge fields. The space charge could lead to polarisation, and consequently, a shift in the transition temperature towards higher values. (c) 2005 Elsevier B.V. All rights reserved.