MAJIS (Moons And Jupiter Imaging Spectrometer) is the visible and infrared imaging spectrometer of the ESA L-Class mission JUICE (JUpiter Icy moons Explorer). MAJIS plays a major role for achieving the JUICE main scientific objectives, which include the compositional study of the Galilean moons, their past and present activity, and its relation with observed surface features. It will also study the composition, structure, chemistry and dynamics of the Jovian atmosphere. MAJIS is composed of two spectral channels: the VIS-NIR (0.5µm-2.35µm), and the IR (2.25µm-5.54µm). Both channels are equipped with a Focal Plane Unit (FPU) mainly including a Teledyne H1RG Focal Plan Array (FPA), one Focal Plane electronics (FPE) and one filter. A dedicated facility was developed at the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) for the characterization of the Flight (FM) and Spare (SM) models of the MAJIS VIS-NIR FPU. The radiometric capabilities of the facility include: (1) the tuning of the monochromatic flux provided to the detector over a four-decade range of intensity, (2) optical configurations for dark conditions, uniform light beam or convergent light beam with the same focal ratio as MAJIS, and (3) relative and absolute radiometric scales at the FPA plane. This work describes the radiometric characterization campaign of the MAJIS VIS-NIR SM FPU and the respective data analysis methods used to derive some of the detector key parameters such as the gain, the dark current, the linearity, the full-well capacity and the operability. A comparison with the performances of the FM VIS-NIR FPU is also provided.