We report an Al0.25Ga0.75N/GaN based lateral field emission device with a nanometer scale void channel.A ～45 nm void channel is obtained by etching out the SiO2 sacrificial dielectric layer between the semiconductor emitter and the metal collector.Under an atmospheric environment instead of vacuum conditions,the GaNbased field emission device shows a low tu-on voltage of 2.3 V,a high emission current of ～40 μA (line current density 2.3mA/cm) at a collector bias VC =3 V,and a low reverse leakage of 3hA at VC =-3 V.These characteristics are attributed to the nanometer scale void channel as well as the high density of two-dimensional electron gas in the AlGaN/GaN heterojunction.This type of device may have potential applications in high frequency microelectronics or nanoelectronics.