Automatic release and vertical transferring of silicon/silicon oxide nanowire arrays with a high integrity are demonstrated by an Ag-assisted ammonia etching method. By adding a water steaming step between Ag-assisted HF/H2O2 and ammonia etching to form a SiOx protective layer sheathing Si nanowires, we can tune the composition of the nanowires from SiOx (0 ≤ x ≤ 2) to Si nanowires. Ag plays a key role to the neat and uniform release of Si/SiOx nanowire arrays from Si wafer in the ammonia etching process. The vertical Si nanowire array device, with both sides having high-quality Ohmic contact, can be transferred to arbitrary substrates, especially on a flexible substrate. The method developed here offers a facile method to realize flexible Si nanowire array functional devices.