An ozone generator (10) has top and bottom chambers (12, 14) interconnected by a vertically extending elongated tubular assembly (16). Assembly (16) has a control electrode (18) within a conductive tube member (20) and separated therefrom by an annular dielectric member (22) which only partly fills the space between items (18, 20). The dielectric member (22) is suspended by an O-ring at its upper end within the top chamber (12) and is free from contact with both the electrode (18) and the tube member (20). Gas flow between the top and bottom chambers (12, 14) is along radially inner and outer annular passageways within the assembly (16) and the top chamber (12) is partitioned into two chambers which respectively communicate with these passageways. The generator (10) may have a plurality of similar assemblies (16) extending in parallel between common top and bottom chambers (12, 14).