The present invention generally relates to methods measuring pinhole determination. In one aspect, a method of measuring pinholes in a stack, such as a TFT stack, is provided. The method can include forming an active layer on a deposition surface of a substrate, forming a dielectric layer over the active layer, delivering an etchant to at least the dielectric layer, to etch both the dielectric layer and any pinholes formed therein and optically measuring the pinhole density of the etched dielectric layer using the active layer.