The results of differential capacitance measurements of P(111)-type silicon electrodes (10 Ω cm) placed in 0·1 M Na 2SO 4 solutions with various pH are given in the paper. The capacitance were determined with the pulse techniques in the frequency range from 1 to 100 kHz. The silicon electrode potential, U, relative to an sce was varied from −0·05 to −0·9 V. It was found that a dispersion of differential capacitance appeared for potentials up to an U ss value. For the potentials U < U ss the experimental differential capacitance values are independent of frequency and of potential variation. The experimental results were interpreted by comparing them with the space charge region capacitance values of silicon.