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Enhanced electroluminescence (EL) has been achieved from the light-emitting devices containing Si quantum dots/SiO₂ multilayers deposited on Si nanowire arrays because of the good antireflection characteristics of Si nanowire structures, which improves the light extraction efficiency. However, it is found that the EL is first enhanced with increasing the depth of the Si nanowires and then reduced to further increase the depth, though it exhibits the lowest reflectance (~3%), which may be due to the increased surface defect states after long time etching, as revealed by electron spin resonance measurements. It is demonstrated that the posthydrogen plasma annealing treatments can passivate the surface defect states which, in turn, improve device performance. The best device shows the turn-on voltage as low as 3.5 V, and the EL intensity of devices on Si nanowire arrays is enhanced 16-fold, compared with that of flat one.