An energy harvesting device comprises a semiconductor device, a first magnet core, and at least one second magnet core. The semiconductor device, disposed in a housing, includes a plurality of first sensors and a plurality of second sensors. The first magnet core, disposed over the semiconductor device, is configured to establish a magnetic field between the first sensors and move with respect to the semiconductor device. The at least one second magnet core, disposed between an inner wall of the housing and the semiconductor device, is configured to establish a magnetic field between the second sensors and move with respect to the semiconductor device.