Semiconductor nanowires (NWs) are gaining significant importance in various biological applications, such as biosensing and drug delivery. Efficient and controlled immobilization of biomolecules on the NW surface is crucial for many of these applications. Here, we present for the first time the use of the CuI‐catalyzed alkyne–azide cycloaddition and its strain‐promoted variant for the covalent functionalization of vertical NWs with peptides and proteins. The potential of the approach was demonstrated in two complementary applications of measuring enzyme activity and protein binding, which is of general interest for biological studies. The attachment of a peptide substrate provided NW arrays for the detection of protease activity. In addition, green fluorescent protein was immobilized in a site‐specific manner and recognized by antibody binding to demonstrate the proof‐of‐concept for the use of covalently modified NWs for diagnostic purposes using minute amounts of material. Click on nanowires: A method for highly reproducible, covalent functionalization of oxidized semiconductor nanowires with peptides and proteins is reported. The method combines silanization with the CuI‐catalyzed and strain‐promoted alkyne–azide cycloaddition (CuAAC and SPAAC) reactions. A protease FRET substrate and green fluorescent protein were site‐specifically immobilized on GaAs nanowires.