In the present work we focus on the investigation by electron spin resonance (EPR) and complementary techniques (such as SEM, ToF-SIMS, XPS) of silicon nanowires produced by metal-assisted chemical etching (MACE). In particular we will report on the impact of the MACE process on the donors (P and As) and on surface passivation processes based on H or S. The efficiency of the passivation processes has been monitored by following the EPR signals of the P b centers at the Si/SiO 2 interface.