He served as Chairman of the SIA Engineering Company; a Director of Agilent Technologies Inc, [Four Soft Ltd] and Norelco UMS Holdings Limited; Executive Director of MediaRing Limited and Tech Group Asia Limited. He serves on the boards of Temasek Holdings (Private) Limited as a Director; AAC Acoustic Technologies Holdings Ltd and Infiniti Solutions Private Limited. He is also a Council Member of the Singapore Business Federation.
On 1 January 2006, Koh became chairman of DBS Bank. He joined DBS as a director on 15 June 2005. He will be stepping down from his current post on 30 April. His replacement is Peter Seah.