ABSTRACT Cao, D.P.; Jian, W.; Huang, Z.H., and Lo, E.Y.M., 2018. Prediction of wave runup on columns of two semisubmersibles models. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1031–1035. Coconut Creek (Florida), ISSN 0749-0208. Water wave runup on columns of semi-submersibles has important implications on negative air-gaps created and slamming forces exerted on the underside of such platforms and their safe operations in rough seas. Many prediction formulas have been developed for wave runup on single vertical columns though none could be directly used for runup predictions on the columns of semi-submersibles due to the more complicated geometrical and diffraction effects. In the present study, small-scale experimental tests and limited numerical simulations using the linear diffraction and CFD solvers were conducted on two typical semi-submersible models...