A high-voltage semiconductor device is provided. The high-voltage semiconductor device includes a substrate; an epitaxial layer and a gate structure; a first conductive type first high-voltage well region and a second conductive type high-voltage well region disposed in the epitaxial layer at opposite sides of the gate structure respectively, wherein the first conductive type is different from the second conductive type; a source region and a drain region; and a stack structure disposed between the gate structure and the drain region, wherein the stack structure includes: a blocking layer; an insulating layer disposed over the blocking layer; and a conductive layer disposed over the insulating layer and electrically connected the source region or the gate structure. A method for manufacturing the high-voltage semiconductor device is also provided.