A reliable flat speaker unit and a speaker device with the same are provided herein. A conductive electrode of a vibrating membrane of the speaker unit is disposed on both utmost sides of the speaker unit to isolate the speaker unit from environmental moisture, which can significantly improve the reliance of the speaker device. A barrier layer can optionally be disposed on the external side of the conductive electrode to further isolating the speaker unit from moisture, which can improve the reliance and the lifetime of the speaker device. In an embodiment, at least a getter is disposed inside the flat speaker unit to absorb moisture therein. The speaker unit at least includes a electret vibrating membrane with a conductive electrode, a plurality of supporting members, and a electrode structure with a plurality of holes.