The synthesis and wurtzite crystalline structure of silicon nanowires (NW) were investigated using chemical vapor deposition (CVD). Si nanowires were synthesized using oxidized substrate by a vapor-liquid-solid (VLS) method. Thermally oxidized Si substrates with an oxide thickness of 1 μm were covered with a 2-3 nm thin gold film by sputtering. The substrate were introduced into a vacuum furnace and heated to a deposition temperature between 500 and 650°C with a constant flow of 100 sccm of hydrogen to ensure thermal equilibrium. 2.5% silane was added to the hydrogen flow in the furnace. NWs were mechanically removed from the substrate, diluted in n-hexane and subsequently deposited on a microscope grid. NWs bridging along the holes of the carbon membrane were analyzed using HRTEM. It was observed that NWs crystallize in wurtzite Si IVA. Result shows that atoms of NWs have tetrahedral coordination in wurtzite structure while the stacking of the tetrahedra varies.