The effect of film thickness on the conduction activation energy and resistivity of flash evaporated Pb0.5Sn0.5Te thin films has been investigated. The conduction activation energy has been found to decrease with an increase in thickness. The observed variation of conduction activation energy with thickness has been explained using Seto's polycrystalline model. The linear reciprocal thickness dependence of electrical resistivity observed has been explained by the "effective mean free path model" of classical size effect. © 1995.