Reconfigurable　intelligent　surface　(RIS)-aided　spatial　modulation　(RIS-SM)　and　its　variants　utilize　the　indices　of　receiver　antennas　and　RIS　grouping　to　transmit　additional　information　bits,　with　the　limited　performance　for　large　inactivated　RIS　elements.　To　address　this　issue,　we　propose　to　exploit　an　activation　mode　index　for　RIS-SM　(AMI-RIS-SM),　where　the　RIS　can　operate　in　different　activation　modes　during　various　time　slots.　In　this　way,　its　activation　mode　index,　coupled　with　the　receiver　antenna　index,　can　transmit　more　information　bits.　Furthermore,　we　propose　maximum　likelihood　(ML)　and　low-complexity　pre-greedy　ML　detections　to　recover　the　transmitted　bits.　We　then　derive　the　bit　error　rate　(BER)　performance　of　the　proposed　AMI-RIS-SM.　The　analytical　and　consistent　simulation　results　show　that　the　proposed　scheme　can　achieve　significant　performance　of　up　to　a　4　dB　gain　over　its　counterparts.