Free-standing silicene, a silicon analogue of graphene, has a buckled honeycomb lattice(1) and, because of its Dirac bandstructure(2,3) combined with its sensitive surface, offers the potential for a widely tunable two-dimensional monolayer, where external fields and interface interactions can be exploited to influence fundamental properties such as bandgap(4) and band character(5) for future nanoelectronic devices(6,7). The quantum spin Hall effect(3), chiral superconductivity(8), giant magnetoresistance(9) and various exotic field-dependent states7 have been predicted in monolayer silicene. Despite recent progress regarding the epitaxial synthesis of silicene(8-10) and investigation of its electronic properties(11,13-15), to date there has been no report of experimental silicene devices because of its air stability issue(16). Here, we report a silicene field-effect transistor, corroborating theoretical expectations regarding its ambipolar Dirac charge transport(17), with a measured roomtemperature mobility of similar to 100 cm(2) V-1 s(-1) attributed to acoustic phonon-limited transport(18) and grain boundary scattering. These results are enabled by a growth-transfer-fabrication process that we have devised-silicene encapsulated delamination with native electrodes. This approach addresses a major challenge for material preservation of silicene during transfer and device fabrication and is applicable to other air-sensitive two-dimensional materials such as germanene(2-4) and phosphorene(19,20). Silicene's allotropic affinity with bulk silicon and its low-temperature synthesis compared with graphene or alternative two-dimensional semiconductors suggest a more direct integration with ubiquitous semiconductor technology.