ECR hydrogen plasma has been studied for removal of the native oxide and for in situ surface cleaning of Si. The process induced changes on electrical properties were inspected with Schottky diode and MOS capacitor structures. Current-Voltage (I-V) measurement of the Schottky diodes showed only a moderate change (about a decade) of the reverse saturation current after the plasma exposure. The deep level majority carrier traps induced by the treatment were measured by Deep Level Transient Spectroscopy (DLTS), and were found to have activation energies of 0.40 eV in the n-type samples and 0.54 eV in the p-type samples. As the plasma exposure time increased, the defect concentration increased and a broad shoulder appeared on the low temperature side. The extent of hydrogen permeation into the silicon was inspected by Capacitance-Voltage (C-V) measurement. Bias-temperature stress measurements of the p-Si Schottky samples reveal redistribution of hydrogen. Polysilicon gate-oxide-silicon samples subject to the hydrogen plasma exposure exhibit negligible change of the interface state density and flatband voltage.