The transient behavior of a trapped electron in the TiO2 sol-gel based gate dielectric layer of a silicon-on-insulator metal-oxide-semiconductor field effect transistor is investigated. Defects in this dielectric layer give rise to microwave resonances that are electrically detected via the channel current. The lifetime of the excited state is inferred from the quality factor of the resonance. A single shot measurement, carried out on the same resonance, is used to characterize the transient behavior and to directly measure the lifetime of the excited state. Possible applications of transient measurements on high-k dielectric layers are discussed.