Vacuum field effect transistors have been envisioned to hold the promise of replacing solid-state electronics when the ballistic transport of electrons in a nanoscale vacuum can enable significantly high switching speed and stability. However, it remains challenging to obtain high-performance and reliable field-emitter materials. In this work, we report a systematic study on the field emission of novel two-dimensional tin selenide (SnSe) with rational design of its structures and surface morphologies. SnSe in the form of atomically smooth single crystals and nanostructures (nanoflowers) is chemically synthesized and studied as field emitters with varying channel lengths from 6 μm to 100 nm. Our study shows that devices based on SnSe nanoflowers significantly improve the performance and enable field emission at a reduced voltage due to a surface-enhanced local electrostatic field, and further lead to nonlinear dependent channel scaling when the channel length is shorter than 600 nm. We measured a record-high short-channel field-enhancement factor of 50 600 for a 100 nm device. Moreover, we investigated the emission stability and measured the fluctuations of the emission current which are smaller than 5% for more than 20 hours. Our results demonstrated a high-performance and highly reliable field emitter based on 2D SnSe nanostructures and we developed an important building block for nanoscale vacuum field effect transistors.