An array substrate for a digital X-ray detector, and an X-ray detector including the same are disclosed, which reduce or minimize a contact resistance between a bias electrode and a PIN diode, and also improve a fill factor of the PIN diode. In the array substrate, a dual bias electrode in which a second bias electrode formed of a transparent conductive material is connected to a first bias electrode that is additionally connected to an upper electrode of the PIN diode, such that total resistance of the bias electrodes is reduced and a line width of the first bias electrode formed of a non-transparent material is reduced, resulting in an increased fill factor of the PIN diode.