A thin film transistor (TFT) includes a semiconductive layer, a first inter-layer drain (ILD) layer, a second ILD layer, and at least one contact hole passing through the first ILD layer and the second ILD layer. The semiconductive layer includes a channel region, a first lightly doped drain (LDD) region, a second LDD region, a first heavily doped drain (HDD) region, and a second HDD region. The at least one contact hole includes a first portion passing through the second ILD layer and a second portion passing through the first ILD layer. The second portion gradually narrows along a direction from a top to a bottom of the first ILD layer.

The present disclosure provides a semiconductor device, including a substrate, a first active region in the substrate, a second active region in the substrate and adjacent to the first active region, an isolation region in the substrate and between the first active region and the second active region, and a dummy gate overlapping with the isolation region, wherein an entire bottom width of the dummy gate is greater than an entire top width of the isolation region.