Exhibit 99.1(a)

genmab_logoa.jpg

APPENDIX Share buy-back programme - Specification for June 2-6, 2025
IssuerDateTime CETQuantityPrice (DKK)Venue
GENMAB A/S02-Jun-202510:00:42 AM51432.50XCSE
GENMAB A/S02-Jun-202510:00:42 AM51431.50XCSE
GENMAB A/S02-Jun-202510:35:18 AM61422.00XCSE
GENMAB A/S02-Jun-202511:15:59 AM61417.00XCSE
GENMAB A/S02-Jun-202512:04:44 PM61420.00XCSE
GENMAB A/S02-Jun-202512:59:59 PM51424.00XCSE
GENMAB A/S02-Jun-202513:51:46 PM51424.00XCSE
GENMAB A/S02-Jun-202514:15:08 PM51423.00XCSE
GENMAB A/S02-Jun-202515:01:49 PM51428.00XCSE
GENMAB A/S02-Jun-202515:21:40 PM51430.00XCSE
GENMAB A/S02-Jun-202515:29:36 PM51427.50XCSE
GENMAB A/S02-Jun-202515:35:07 PM51425.50XCSE
GENMAB A/S02-Jun-202515:45:22 PM71430.00XCSE
GENMAB A/S02-Jun-202515:55:11 PM51422.50XCSE
GENMAB A/S02-Jun-202516:06:18 PM71414.50XCSE
GENMAB A/S02-Jun-202516:23:02 PM11414.00XCSE
GENMAB A/S02-Jun-202516:23:26 PM51415.00XCSE
GENMAB A/S02-Jun-202516:36:48 PM51420.50XCSE
GENMAB A/S02-Jun-202516:46:32 PM11422.50XCSE
GENMAB A/S02-Jun-202516:46:37 PM11422.50XCSE
GENMAB A/S02-Jun-202516:46:58 PM31422.50XCSE
GENMAB A/S02-Jun-202516:47:57 PM21423.50XCSE
GENMAB A/S03-Jun-202510:19:07 AM51411.50XCSE
GENMAB A/S03-Jun-202510:19:08 AM51410.50XCSE
GENMAB A/S03-Jun-202510:58:43 AM51400.00XCSE
GENMAB A/S03-Jun-202511:38:14 AM51391.50XCSE
GENMAB A/S03-Jun-202512:03:23 PM51390.00XCSE
GENMAB A/S03-Jun-202512:50:25 PM51392.00XCSE
GENMAB A/S03-Jun-202513:42:38 PM61397.50XCSE
GENMAB A/S03-Jun-202514:27:34 PM61399.50XCSE
GENMAB A/S03-Jun-202515:01:23 PM61395.50XCSE
GENMAB A/S03-Jun-202515:28:03 PM71390.00XCSE
GENMAB A/S03-Jun-202515:33:17 PM51373.50XCSE
GENMAB A/S03-Jun-202515:41:34 PM51391.50XCSE
GENMAB A/S03-Jun-202515:46:45 PM51395.00XCSE
GENMAB A/S03-Jun-202515:56:42 PM61397.50XCSE
GENMAB A/S03-Jun-202516:07:16 PM51395.50XCSE
GENMAB A/S03-Jun-202516:24:32 PM71398.00XCSE
GENMAB A/S03-Jun-202516:37:54 PM51397.50XCSE
GENMAB A/S03-Jun-202516:46:55 PM51400.00XCSE
GENMAB A/S03-Jun-202516:49:01 PM21400.00XCSE
1



genmab_logoa.jpg

APPENDIX Share buy-back programme - Specification for June 2-6, 2025
GENMAB A/S04-Jun-202509:42:14 AM51429.00XCSE
GENMAB A/S04-Jun-202509:44:00 AM51432.00XCSE
GENMAB A/S04-Jun-202510:18:06 AM51432.00XCSE
GENMAB A/S04-Jun-202511:00:40 AM51435.00XCSE
GENMAB A/S04-Jun-202511:20:04 AM51432.50XCSE
GENMAB A/S04-Jun-202512:14:50 PM61420.50XCSE
GENMAB A/S04-Jun-202513:07:34 PM51422.50XCSE
GENMAB A/S04-Jun-202514:01:16 PM21432.00XCSE
GENMAB A/S04-Jun-202514:01:16 PM51432.00XCSE
GENMAB A/S04-Jun-202514:45:04 PM61433.50XCSE
GENMAB A/S04-Jun-202515:16:28 PM61442.00XCSE
GENMAB A/S04-Jun-202515:32:41 PM61445.50XCSE
GENMAB A/S04-Jun-202515:37:46 PM51450.50XCSE
GENMAB A/S04-Jun-202515:47:59 PM61447.50XCSE
GENMAB A/S04-Jun-202515:57:37 PM61439.00XCSE
GENMAB A/S04-Jun-202516:10:39 PM61434.00XCSE
GENMAB A/S04-Jun-202516:25:16 PM51441.00XCSE
GENMAB A/S04-Jun-202516:41:23 PM61434.00XCSE
GENMAB A/S04-Jun-202516:48:44 PM51438.50XCSE
GENMAB A/S06-Jun-202509:33:12 AM51446.50XCSE
GENMAB A/S06-Jun-202509:33:36 AM51445.50XCSE
GENMAB A/S06-Jun-202510:20:15 AM61449.50XCSE
GENMAB A/S06-Jun-202511:01:14 AM51455.00XCSE
GENMAB A/S06-Jun-202511:45:03 AM61450.00XCSE
GENMAB A/S06-Jun-202512:33:40 PM21443.00XCSE
GENMAB A/S06-Jun-202512:33:42 PM31443.00XCSE
GENMAB A/S06-Jun-202513:00:06 PM11444.50XCSE
GENMAB A/S06-Jun-202513:01:56 PM41444.50XCSE
GENMAB A/S06-Jun-202513:51:50 PM51440.50XCSE
GENMAB A/S06-Jun-202514:33:47 PM71441.00XCSE
GENMAB A/S06-Jun-202515:09:25 PM51442.00XCSE
GENMAB A/S06-Jun-202515:28:00 PM61438.50XCSE
GENMAB A/S06-Jun-202515:36:39 PM61442.50XCSE
GENMAB A/S06-Jun-202515:49:53 PM51442.50XCSE
GENMAB A/S06-Jun-202515:52:33 PM51442.50XCSE
GENMAB A/S06-Jun-202516:04:06 PM51446.00XCSE
GENMAB A/S06-Jun-202516:20:41 PM61444.00XCSE
GENMAB A/S06-Jun-202516:33:29 PM51444.00XCSE
GENMAB A/S06-Jun-202516:44:45 PM51442.50XCSE
GENMAB A/S06-Jun-202516:48:22 PM31444.50XCSE
2