The authors present the impact of fast charging and the ambient on the intrinsic mobility of a WS2 field-effect transistor (FET) by fast pulsed current-voltage (I-V) measurement. Conventional electrical analysis using the direct current (DC) I-V method in air causes charge trapping during measurement, making it impossible to determine the intrinsic device characteristics. Thus, the authors employed the fast pulsed I-V method in vacuum to minimize fast transient charging and interfacial redox-induced charging during measurement. The authors obtained field-effect mobility values of 16.27 and 14.92 cm(2)/V s in vacuum and air, respectively, using the fast I-V technique; these mobility values were 52%-65% higher than those obtained by the DC method in vacuum and air, respectively. The authors also determined the intrinsic mobility of the WS2 FET using the threshold voltage shift with pulse amplitude. (C) 2017 American Vacuum Society.