Thermoelectronic energy converter device, comprising: - an electron emitter being adapted for a temperature-dependent release of electrons, - an electron collector being adapted for collecting the electrons, wherein the electron collector is spaced from the electron emitter by an evacuated gap, and - a gate electrode being arranged between the electron emitter and the electron collector for subjecting the electrons in the gap between the electron emitter and the electron collector to an accelerating electric potential, said gate electrode having a plurality of electrode openings being arranged for transmitting electrons running from the electron emitter to the electron collector, wherein - the electrode openings have a cross-sectional dimension being equal to or smaller than five times the width of the gap between the electron emitter and the electron collector, - the width of the gap between the electron emitter and the electron collector is below 0.5 mm, characterized in that - a magnetic field device is arranged for creating a magnetic field with magnetic field lines extending between the electron emitter and the electron collector (11, 21), such that at least a portion of the magnetic field lines pass through the electrode openings, wherein - at least one auxiliary gate electrode is arranged between the electron emitter and the electron collector (11, 21) at or near a surface of the electron collector for suppressing electron charge effects at the surface of the electron collector by applying a positive voltage of a dc source to the auxiliary gate electrode relative to the electron collector and/or at least one shielding electrode is arranged between the electron emitter and the electron collector (11, 21) on the side of the gate electrode facing to the electron emitter, said shielding electrode being electrically insulated relative to the gate electrode by an insulating layer and connected with an additional voltage source, which is arranged and adapted to form a field barrier around the gate electrode, thereby forcing the electrons to electron paths through the electrode openings. - an electron emitter being adapted for a temperature-dependent release of electrons, - an electron collector being adapted for collecting the electrons, wherein the electron collector is spaced from the electron emitter by an evacuated gap, and - a gate electrode being arranged between the electron emitter and the electron collector for subjecting the electrons in the gap between the electron emitter and the electron collector to an accelerating electric potential, said gate electrode having a plurality of electrode openings being arranged for transmitting electrons running from the electron emitter to the electron collector, wherein - the electrode openings have a cross-sectional dimension being equal to or smaller than five times the width of the gap between the electron emitter and the electron collector, - the width of the gap between the electron emitter and the electron collector is below 0.5 mm, characterized in that - a magnetic field device is arranged for creating a magnetic field with magnetic field lines extending between the electron emitter and the electron collector (11, 21), such that at least a portion of the magnetic field lines pass through the electrode openings, wherein - at least one auxiliary gate electrode is arranged between the electron emitter and the electron collector (11, 21) at or near a surface of the electron collector for suppressing electron charge effects at the surface of the electron collector by applying a positive voltage of a dc source to the auxiliary gate electrode relative to the electron collector and/or at least one shielding electrode is arranged between the electron emitter and the electron collector (11, 21) on the side of the gate electrode facing to the electron emitter, said shielding electrode being electrically insulated relative to the gate electrode by an insulating layer and connected with an additional voltage source, which is arranged and adapted to form a field barrier around the gate electrode, thereby forcing the electrons to electron paths through the electrode openings.