A locking device for securing a heat sink to a heat generating component includes a locking plate, a plurality of locking feet each pivotably attached to the locking plate and a plurality of locking members attached to the locking feet. Adjacent two of the plurality of locking feet are capable of rotating towards each other from a first position at which the locking feet are located apart from each other with the locking members defining a first mounting position to a second position at which the locking feet are stacked together with the locking members defining a second mounting position.