Provided are electrode-connecting structures or semiconductor devices, including a lower device including a lower substrate, a lower insulating layer formed on the lower substrate, and a lower electrode structure formed in the lower insulating layer, wherein the lower electrode structure includes a lower electrode barrier layer and a lower metal electrode formed on the lower electrode barrier layer, and an upper device including an upper substrate, an upper insulating layer formed under the upper substrate, and an upper electrode structure formed in the upper insulating layer, wherein the upper electrode structure includes an upper electrode barrier layer extending from the inside of the upper insulating layer under a bottom surface thereof and an upper metal electrode formed on the upper electrode barrier layer. The lower metal electrode is in direct contact with the upper metal electrode.