NFL Network insider Jason La Canfora reported Friday that Boss signed a four-year deal worth $16 million, with $8 million guaranteed, according to a league source.
The Raiders brought in Boss for a workout Wednesday and signed him after restructuring contracts to get under the salary cap.
Boss had 35 catches for 531 yards and five touchdowns for the New York Giants last season. He has 119 catches for 1,600 yards and 18 touchdowns in four NFL seasons.
The Associated Press contributed to this report.