Highly stable organic electroluminescent devices based on vapor‐deposited Alq thin films have been achieved. The improvement in stability is derived from several factors including: (1) a multilayer thin‐film structure with a CuPc stabilized hole‐injection contact, (2) a hole‐transport diamine layer using a naphthyl‐substituted benzidine derivative, and (3) an ac drive wave form. These emissive devices have shown an operational half‐lifetime of about 4000 h from an initial luminance of 510 cd/m2.