An electron beam sterilizing device, comprises: an electron-generating filament; a beam-shaper; an output window; a high-voltage supply, capable of creating a high-voltage potential between the electron-generating filament and the output window, for acceleration of electrons; a high-voltage supply for driving current through the electron-generating filament; a control unit for controlling the operation of the electron beam sterilizing device. The electron beam sterilizing device has at least three operational states which include: an OFF-state, where there is no drive current through the electron-generating filament; an ON-state, where the electron-generating filament is kept at a temperature above the emission temperature so as to generate electrons for sterilization; and a standby state, between the OFF-state and ON-state, where the electron-generating filament is kept at a predetermined temperature just below the emission temperature. The control unit controls the device to assume the standby state.