The authors examine the effects of adsorption of four thiolated molecules ( H S – C ₁₀ H ₂₁ , H S – C ₁₁ H ₂₂ O H , H S – C ₁₀ H ₂₀ C O O H , and H S – C ₂ H ₄ C ₄ F ₉ ) on the electrical characteristics of single-walled carbon nanotube network FETs (SNFETs). Work function of the electrodes was measured before and after molecule adsorption. Schottky barrier energy extraction for SNFETs was also performed and the results provide direct evidence that the device characteristics of SNFETs after SAM adsorption are altered primarily due to the change in energy-level alignment between the Au and SWNTs, which thus provides an effective methodology for the tuning and performance optimization of these devices in a controllable way.