A combination study of electrochemical measurements and reflection high energy electron diffraction (RHEED) surface analysis experiments in a vacuum was first demonstrated to characterize a p-Si(111): H/ionic liquid interface. Mott-Schottky plot analysis was made to successfully not only evaluate the acceptor density and flat band potential of the p-Si(111):H, but also get some insight into its surface states. Furthermore, the electric double layer capacitance and specific adsorption properties at the IL/Si (111):H interface as well as the electrochemical interface stability will be discussed in this paper. (C) 2016 Elsevier B.V. All rights reserved.