We examined the experimental observation of negative differential resistance (NDR) in GeSn/GeSiSn double barrier structure (DBS) toward resonant tunneling diode (RTD) application from both theoretical and experimental perspectives. From the theoretical simulation, we found that RTD operation is possible by well-designed thicknesses of GeSn and GeSiSn layers. Furthermore, the appearance of NDR was experimentally demonstrated in GeSn/GeSiSn RTDs. Finally, we discussed possible approaches to improve their RTD performance.