The semiconductive and photoelectrochemical properties of reduced polycrystalline $SrTiO_3$ electrode have been studied in 1 N NaOH solution by using AC impedance and potentiodynamic techniques. The compacted $SrTiO_3$ powder were sintered for 6 h at 1400℃, and then reduced for 2 h at the temperature range of 800℃ to 1200℃ under hydrogen atmosphere. The AC impedance measurements were carried out by superimposing an AC voltage of 5 mV amplitude on a DC bias of-2000 to $1000mV_{SCE}$ over a frequency range of 5 to 10000Hz. The equivalent circuit is found to consist of a series connection of a parallel RC circuit of electrode/electrolyte interface and a total resistance of the electrolyte and the electrode from Bode and admittance plots. The capacitance decreased with increasing applied potential and frequency. The donor concentration $N_d$ of the electrode increased from $2.3×10^{18}$ to $2.2×10^{19}cm^{-3}$ with increasing reduction temperature from 800℃ to 1200℃. The flat-band potential $V_{fb}$ was found to be about 1376 to $1468mV_{SCE}$. The effects of frequency and applied potential on the semiconductive properties of $SrTiO_3$ electrodes were discussed in term of the change of donor concentration. The on-set potential at which the photocurrent begin to occur, appeared to shift toward flat-band potential with increasing light intensity.
