This paper presents the results of an experimental and theoretical investigation of carrier transport and interface state kinetics at grain boundaries in silicon. The grain-boundary interface has been modelled numerically using finite-element methods, and measurements of transient capacitance together with current-voltage characteristics have been recorded over a temperature range from 100K to 300K. Among our findings is that thermionic-field emission from grain-boundary interface states, which has been ignored in earlier treatments, can play a dominant role in transport phenomena for

cm
-3V at T = 300K, or

cm-
-3V at 130K, where N is the bulk silicon doping concentration, and V is the voltage applied across the grain boundary.