A method for fabricating a polysilicon silicon liquid crystal display device is disclosed in which a contact hole connecting source and drain electrodes to an active layer is formed without a stepped portion. An insulation layer containing a porous silicon nitride layer is formed. Wet etching the contact hole through the porous silicon nitride layer and an underlying silicon oxide layer does not generate the stepped portion as the etch rates of the porous silicon nitride layer and the silicon oxide layer are the same. Because the stepped portion is not generated at a contact hole, disconnection of source and drain electrodes formed in the contact hole is prevented, thereby preventing deterioration of the liquid crystal display device from occurring.