We have studied the electrical properties of hydrogenated nanocrystalline silicon/crystalline silicon heterojunction diode, focusing on the band offsets and electron transport mechanisms. Capacitance-voltage ͑C-V͒ analysis reveals that the band discontinuity mainly exists on the valence-band side, and an interface charge density on the order of 10 11 cm −2 is estimated via the numerical C-V matching technique. Temperature-and bias-dependent transport mechanisms have been clarified by dark current-voltage-temperature measurements, and the extracted parameters indicate a transition from nontunneling to tunneling dominant transport from 350 to 20 K.