A lead frame of high quality which can endure direct bonding to a semiconductor element, and a semiconductor device of high reliability which utilizing the lead frame. A lead frame includes a plurality of connected units, each unit including a pair of lead portions arranged spaced apart and opposite from each other, for mounting a semiconductor element and electrically connecting to a pair of electrodes of the semiconductor element respectively. The lead portions respectively include an element mounting region arranged on a surface thereof to mount the semiconductor element, and a groove extending from opposing end surfaces of each of the pair of lead portions, in a direction away from the end surfaces and bending in a surrounding manner along outer periphery of the element mounting region.