Silicon nanowire (Si NW)-based field effect transistors (FETs) have shown great potential as biosensors (bioFETs) for ultra-sensitive and label-free detection of biomolecular interactions. Their sensitivity depends not only on the device properties, but also on the function of the biological recognition motif attached to the Si NWs. In this study, we show that SiNWs can be chemically functionalized with Ni:NTA motifs, suitable for the specific immobilization of proteins via a short polyhistidine tag (His-tag) at close proximity to the SiNW surface. We demonstrate that the proteins preserve their function upon immobilization onto SiNWs. Importantly, the protein immobilization on the Si NWs is shown to be reversible after addition of EDTA or imidazole, thus allowing the regeneration of the bioFET when needed, such as in the case of proteins having a limited lifetime. We anticipate that our methodology may find a generic use for the development of bioFETs exploiting functional protein assays because of its high compatibility to various types of NWs and proteins.