High performance pentacene organic thin film transistors (OTFT) were designed and fabricated using SiO2 deposited by electron beam evaporation as gate dielectric material.Pentacene thin films were prepared on glass substrate with S-D electrode patte made from ITO by means of thermal evaporation through self-organized process.The threshold voltage VTH was -2.75±0.1V in 0-50V range,and that subthreshold slopes were 0.42±0.05V/dec.The field-effect mobility (μEF) of OTFT device increased with the increase of VDS,but the μEF of OTFT device increased and then decreased with increased VGS when VDS was kept constant.When VDS was -50V,on/off current ratio was 0.48x105 and subthreshold slope was 0.44V/dec.The μEF was 1.10cm2/(V-s),threshold voltage was -2.71V for the OTFT device.