A novel concrete-filled steel tubular (CFST) column with semi-circular stiffeners welded in the inner side of the square tube is proposed in this study. The semi-circular stiffeners are developed based on the confinement mechanism in square CFST columns and aim to strengthen the confinement effect on concrete in the whole cross-section area, therefore improving the overall structural performance of the composite column. The section is also flexible to use different grades of concrete in the core and cell regions. Experimental investigations on axial compressive behaviour of the semi-circle stiffened concrete-filled steel tubular (SCS-CFST) columns as well as the corresponding hollow section columns were carried out. High strength steel Q690 and two concrete grades C40 and C90 were adopted for the test specimens. Various parameters including steel tube thickness, cross-section slenderness, combination of different concrete grades as well as semi-circular stiffener size were investigated. The test results showed that the stiffened hollow sections achieved significantly higher compressive strength with delayed local buckling failure compared to the unstiffened counterparts. SCS-CFST columns, particularly for those with C40 infilled in the core region and C90 infilled in the cell region, presented significantly enhanced compressive strength and ductility compared to the corresponding normal unstiffened CFST columns. The applicability of existing design equations was evaluated for the novel SCS-CFST columns. A new design approach considering the confinement effect in different regions was proposed and exhibited good predictions.