Semiconductor device and manufacturing method thereof

An embodiment of the invention discloses a semiconductor device and a manufacturing method thereof. The semiconductor device comprises a semiconductor substrate, an active region arranged on the semiconductor substrate, wherein the active region has a grid electrode, a source electrode and a drain electrode; and a closed metal ring structure arranged on the semiconductor substrate and used for encircling the active region and receiving voltage to form a depletion isolation layer. The depletion isolation layer is formed through depletion of an electric field, so that defects of an existing isolation process no longer exist; different depths of depletion isolation layers can be formed by adjusting the voltage applied to the closed metal ring structure, so that isolation depth is controllable, and isolation effect is good; the closed metal ring structure is thin, so that obvious planarization problem cannot be caused; and the closed metal ring structure is high in reliability, is simple in manufacturing process,