The present invention relates to an array substrate for a flat display device and a method for fabricating the same, in which a number of masks is reduced for reducing a cost and improving a device performance. The array substrate includes a gate electrode formed on an insulating substrate, a gate insulating film formed on an entire surface of the insulating substrate including the gate electrode, an active layer formed on the gate insulating film opposite to the gate electrode having a stack of a polysilicon layer and an amorphous silicon layer each having a width greater than the gate electrode, a source electrode and a drain electrode separated from each other at a portion of the active layer and formed over the active layer with an ohmic contact layer disposed therebetween, an interlayer insulating film formed on an entire surface of the insulating substrate having a contact hole to expose a predetermined portion of the drain electrode, and a pixel electrode connected to the drain electrode through the contact hole.