We have investigated tunable threshold voltage in solution-processed single-walled carbon nanotube thin-film transistors (SWCNT TFTs) employing a simple and reproducible method of chemical encapsulation. Compared to a pristine one, SWCNT TFTs encapsulated with ammonium hydroxide (NH4OH) and nitric acid (HNO3) exhibit a negative shift and a positive shift in threshold voltage, respectively. Such results can be explained by the modification of the energy band at the interface between the source metal electrode and the SWCNT network. By using the Y-function method, we also characterized electrical properties such as field-effect mobility, threshold voltage, and contact resistance for TFTs treated with NH4OH or HNO3. The technique to favorably tune threshold voltage in solution-processed SWCNTs is significant for constituting CNT-based nanoelectronics. (C) 2015 Elsevier B.V. All rights reserved.