Phenothiazine radical cation PTH+. and phenothiazine dication PTH2+ produced by photoinduced electron transfer in phenothiazine/semiconductor systems have been studied by using ESR, UV-visible absorption, and fluorescence spectroscopic methods, It is found that the PTH+. was generated by electron transfer from (PTH)-P-1* and (PTH)-P-3* to the conduction band of the semiconductors besides PTH+. resulted in the photoionization of PTH as well as PTH2+ produced by electron transfer from PTH+. to the conduction band of the semiconductors successively. Very significant supplementary information provided by UV-visible absorption, ESR, and resonance Raman spectra of PTH+. and PTH2+, which were obtained by oxidation of PTH with lead tetraacetate, not only confirmed the two-step mono-electron-transfer mechanism proposed for interpretation of electron-transfer processes in PTH/semiconductor systems but also demonstrated that the two successive electron-transfer steps were corresponding to the removal of a p-electron at the nitrogen atom and a p-electron at the sulfur atom in the PTH molecule, respectively. Consequently, the nonplanar configuration of the PTH molecule changed into a planar configuration of the PTH2+.