A thermoelectronic energy converter device (100) comprises an electron emitter (11) being adapted for a temperature-dependent release of electrons (1), an electron collector (21) being adapted for collecting the electrons (1), wherein the electron collector (21) is spaced from the electron emitter (11) by an evacuated gap (2), a gate electrode (31) being arranged between the electron emitter (11) and the electron collector (21) for subjecting the electrons (1) in the gap (2) to an accelerating electric potential, wherein the gate electrode (31) has a plurality of electrode openings (34) being arranged for transmitting electrons (1) miming from the electron emitter (11) to the electron collector (21), and a magnetic field device (50) being arranged for creating a magnetic field with magnetic field lines extending between the electron emitter and the electron collector (11, 21), wherein the magnetic field device (50) is arranged such that at least a portion of the magnetic field lines pass through the electrode openings (34). Furthermore, a method of converting energy using the thermoelectronic energy converter device (100) is described.