A method for manufacturing multi-gate transistor device includes providing a semiconductor substrate having a patterned semiconductor layer, a gate dielectric layer and a gate layer sequentially formed thereon, forming a multiple insulating layer sequentially having a first insulating layer and a second insulating layer and covering the patterned semiconductor layer and the gate layer, removing a portion of the multiple insulating layer to simultaneously form a first spacer around the gate layer and a second spacer around the patterned semiconductor layer, removing the second spacer to expose a portion of the first insulating layer covering the patterned semiconductor layer and simultaneously removing a portion of the first spacer to form a third spacer around the gate layer, and removing the exposed first insulating layer to expose the patterned semiconductor layer.