An organic light emitting display which is constructed with a TFT substrate having an insulating substrate and a TFT that has at least a source electrode and a drain electrode, a lower electrode formed on the TFT substrate and connected to one of source/drain electrodes, an insulating layer having an opening that exposes a portion of the lower electrode, an organic thin film layer formed on the exposed portion of the lower electrode and the insulating layer, and an upper electrode formed on the organic thin film layer, wherein the insulating layer has a taper angle less than 40° at an edge of the opening, and a step less than or equal to 3,000 Å is formed between the lower electrode and the organic thin film layer. The organic light emitting display can prevent device failure.