We report on rapid thermal reduction of inkjet-printed Cu interconnects in nitrogen and hydrogen mixture ambient to change the insulating Cu2O to conductive Cu for solution-based all printable thin film transistors fabricated on a glass substrate. By ink-jetting and rapid thermal annealing of nano Cu ink with an average size of similar to 6 nm, we were able to obtain directly patterned Cu interconnects with resistivity of 2.2 x 10(-6) X cm and line width of similar to 50 mu m. Synchrotron x-ray scattering and x-ray photoelectron analysis showed that as-printed Cu interconnect, which existed in the Cu2O phase was completely transformed to metallic Cu interconnects after rapid thermal annealing due to effective reduction by H-2 gas and sintering of inkjet-printed Cu that have a lower melting point than bulk Cu. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3615825] All rights reserved.