The experimental and numerical investigations of the hydrodynamic response on 3-column and 4-column semi-submersible floaters with the same displacement, supporting a wind turbine in regular and random waves have been carried out in the present study. Experiments have been conducted in a laboratory wave flume using 1:75 scale models with the catenary mooring system. The numerical simulations have been performed for identical waves using a panel method based hydrodynamic software, Ansys-AQWA. The simulations were performed on prototype and were validated against the scaled up measurements. The simulated responses compare reasonably well with experiments. It was found that the 4-Column semi-submersible has lower hydrodynamic response and it is more suitable to support a floating wind turbine as compared to 3-column semi-submersible. © 2020 Informa UK Limited, trading as Taylor & Francis Group.