1. A luminescent device comprising: a thin film transistor provided over an insulating surface of a substrate; a luminescent element electrically connected with said thin film transistor, said luminescent element comprising an organic compound layer, an anode and a cathode, said cathode containing an alkaline metal; at least one insulating layer provided between said thin film transistor and said luminescent element and selected from the group consisting of an insulating layer adsorbing said alkaline metal and an insulating layer preventing diffusion of said alkaline metal.