The gas discharge electron gun contains a cold cathode with a concave emission surface, a cathode electrode that covers it, a hollow anode, and a beam transport channel with a magnetic focusing lens located on it. The cold cathode has a limited emission surface, which is (90±5) % of the transverse size of the discharge gap, covered by a truncated cone-shaped near-cathode electrode, the surface of which is tangent to the concave emission surface of the cathode, and the cathode is made of a material with a high coefficient of secondary ion-electron emission.