Transient phenomena observed at the semiconductor-aqueous electrolyte interface were reviewed and theoretical formulation were presented. Among several transients, the photocurrent transient (PCT) and photocapacitance transient (CAPT) were focused because they are complimentary with each other. Namely, the former reflects the system turning from the static to steady state while the latter measured after the light is turned off reflects the reverse process. The origins of transients were classified into several cases, depending on light intensity, electrolyte pH and external bias. The PCT observed at the intermediate pH (10~12) and intermediate light intensity was ascribe to the nature of oxidation products of water. If hydrogen peroxides keep absorbing on the surface partly due to a lack of desorption force and partly due to its stability on the surface, some of them are converted to oxygens by charge exchange with OH^- and some of them are directly converted to oxygens by the chemical reaction with themselves. Therefore, if oxygens also keep absorbing, only source of the current flow is the charge exchange between H₂O₂ and OH^- because oxygens impede further hole transfer. In other words, the changing rate of H₂O₂ determines the PCT from which the charge exchange rate can be estimated.