This paper presents the formulas of 1/f noise in Schottky barrier diodes under reverse bias condition. The derived formulas show that the electron density near the metal-semiconductor interface plays an important role in determining the power spectral density of 1/f noise current in Schottky diodes under reverse bias. The formulas give information on how to calculate the low-frequency noise in metal-semiconductor (or oxide)-metal devices such as resistive switching devices or memristors which have structures of two back-to-back Schottky barrier diodes as well as in the reverse-biased Schottky diodes. The formulas show that the power spectral density of the flicker noise in reverse-biased Schottky barrier diodes increases proportional to the square of the dc current in thermionic emission-limited condition. (c) 2011 Elsevier Ltd. All rights reserved.