The effect of light doping on the phase transition to the ferroelectric state in BaTiO₃ has been studied using synchrotron radiation at Daresbury Laboratory, UK. The results indicate that the presence of dilute impurities, which turn BaTiO₃ from a wide band-gap intrinsic semiconductor into an extrinsic n-type semiconductor, changes the transition from a discontinuous to a continuous one, and produces large spatial variation in magnitude of the electric polarization in both the high- and low-temperature phases; these fluctuations were barely detectable in the pure, annealed material.