Semiconductors are an important category of materials involved in many applications in modern society. One such application revolves around the search for efficient and sustainable forms of energy, where in the use of semiconductors to assist conversion of light to electrical energy. Photoelectrochemical solar cell, though finding meagre application in energy harvesting through photovoltaic route, can be used as a tool to identify solid liquid interaction in presence of incident radiation to find out important material parameters. One such important parameter of PEC system is a flat band potential which relates bending of energy bands of semiconductor to develop a barrier separating photo- generated carriers. In this article, the authors have determined the flat-band potential of a crystalline semiconductor photoelectrode using the Mott–Schottky plot, which relates semiconductor–electrolyte interfacial capacitance to voltage. To demonstrate this approach we used a crystalline p-type NbSe2 semiconductor electrode having a bandgap of 1.42 eV in an electrolyte of 0.025M I2+0.1M K4[Fe(CN)6]+0.1M K3[Fe(CN)6] with redox potential of 0.28 V. LCR meter with a suitable equivalent circuit, was used to extract interfacial capacitance data (C), which was then plotted with the electrode voltage via the Mott–Schottky equation (C−2SC versus VSCE). From the x-axis intercept the flat-band potential was determined to be 0.66 V. The semiconductor parameter values come in the potential range of leading chalcogenides as a semiconductor crystals which can be suitable for photo electrochemical solar cell in the near future.