<p>Semi-submersible platforms operating in deep seas encounter complex environmental conditions, making experimental studies on their global performance essential for new platform designs. Model tests were conducted to examine the 6-DOF motion characteristics of a conceptual semi-submersible platform equipped with a hollow moonpool (SPHM). The experimental results indicate that heave motions of the SPHM demonstrate suboptimal performance, potentially due to the natural heave period coinciding with the predominant wave energy range in the South China Sea. Furthermore, parametric rolling was observed during both regular and irregular wave tests and analyzed through Mathieu’s equation. The analysis reveals that parametric rolling of the SPHM exhibits primarily low-frequency motion with substantial amplitudes, with its period matching the natural roll period. Notably, parametric rolling persists for only several natural roll periods of the platform, leading to considerable variance in roll motions.</p>