Mechanical bonding energies of oxygen plasma treated and room-temperature wafer bonded silicon surfaces have been measured as a function of storage time in parallel with measurements of electrical interface properties. The surface energy increases with time dependence similar to that of decreasing interface state concentration. The current vs voltage behavior reveals the existence of mobile ions. We suggest that these mobile charges, after the reaction with the interface states, give rise to the increased surface energy responsible for bonding. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3355288] All rights reserved.