Pressure-balanced external Ag/AgCl electrodes have been extensively used for electrochemical measurements in high-temperature aqueous experiments. A simple design is suggested that can be available in temperatures where polymer-based materials cannot be applied to, as an electrode body. In this design, the poly(tetrafluoroethylene) tube-ceramic tube junction at the low-temperature region and ceramic tube-ceramic plug junction jointed by brazing in the hot-temperature region play crucial roles. The potential of the KCl-buffered external Ag/AgCl electrode was characterized by estimating the thermal liquid junction potential (TLJP) occurring from the thermal diffusion of buffered ionic species existing in the filling solution. The potential of the thermoelectrochemical cell, Ag(T-0)/AgCl(T-0)/KCl(T-0)/KCl(T)/SHE(T), was divided into the sum of the isothermal potentials and TLJP. The TLJP for the Soret steady state was estimated by adopting Macdonald et al.'s work [J. Electrochem. Soc., 126, 1618 (1979)] and by calculating the heat of transport after Agar et al.'s theory [J. Phys. Chem., 93, 2079 (1989)], and Kirkwood et al.'s linear response theory [J. Chem. Phys., 18, 857 (1960)]. The potential depression at the low-temperature region, which resulted from the thermal diffusion, was also calculated. The calculated potential of the KCl-buffered external Ag/AgCl electrode together with the experimental data was presented. (C) 2004 The Electrochemical Society.