This thesis introduces a new route to control the structure of semiconductor nanowires using surface chemistry. Specifically, in Au-catalyzed Si nanowire growth using hydride species (Si₂H₆) as growth precursors, we demonstrate that the surface hydrogen existing on the nanowires sidewalls affects the growth morphology. First, we show the spectroscopic evidence of atomic hydrogen bonded to sidewall surface of Si nanowires in real-time in situ during growth and correlate their relative change with different growth orientations and planar defect generation. By introducing additional atomic hydrogen during the <111>-oriented nanowire growth with intrinsically low hydrogen concentration, we confirm that the growth orientation changes from <111> to <112> orientation. We also show that the transient change in the nanowire growth conditions (i.e., substrate temperature and precursor pressure) can rationally induce the planar defects such as twin boundary or stacking fault in Si nanowires at user-defined position. These findings provide important insight into the vapor-liquid-solid technique for nanowire growth and identify new possibilities for systematically controlling their structures in general.