The anions PhS(-) and PhSe(-) obtained from cathodic reduction of diorganodichalcogenides, substitute Cl in trimethylchlorosilane with relative rates k(Se)/k(S) = 9.3 to give trimethylsilylphenylsulfide and trimethylsilylphenylselenide; this reaction, carried out in the presence of a carbonyl compound, results in trimethylsilyl ethers of hemithio- (seleno-)ketals and acetals.