A sub-module (200, 600) for use in a multilevel modular converter, the sub-module (200, 600) comprising: at least one energy storage device, a sub-module resistor, and a switch arranged in series with the sub-module resistor, wherein the switch comprises a series connection of semiconductor switching elements and a potential divider, the series of semiconductor switching elements comprising a first switching element and a second switching element; the first switching element comprising a first gate terminal that is configured to control a state between a first source terminal and a first drain terminal; the second switching element comprising a second gate terminal that is configured to control a state between a second source terminal and a second drain terminal; the potential divider having a first resistance (Rg) connected in parallel to a first capacitor (Cs) and a second resistance (Rs) connected in parallel to a second capacitor (Cg), wherein one end of the first resistance (Rg) is connected to the first source terminal and another end of the first resistance (Rg) is connected to the second gate terminal, and wherein one end of the second resistance (Rs) is connected to the first drain terminal and another end of the second resistance (Rs) is connected to the second gate terminal; the potential divider connecting an output of the first switching element to the second gate terminal of the second switching element such that a proportion of a drain-source voltage of the first switching element is configured to be provided as a gate voltage to the second gate terminal; wherein the energy storage device is arranged in parallel with the series connection of the switch and the sub-module resistor. at least one energy storage device, a sub-module resistor, and a switch arranged in series with the sub-module resistor, wherein the switch comprises a series connection of semiconductor switching elements and a potential divider, the series of semiconductor switching elements comprising a first switching element and a second switching element; the first switching element comprising a first gate terminal that is configured to control a state between a first source terminal and a first drain terminal; the second switching element comprising a second gate terminal that is configured to control a state between a second source terminal and a second drain terminal; the potential divider having a first resistance (Rg) connected in parallel to a first capacitor (Cs) and a second resistance (Rs) connected in parallel to a second capacitor (Cg), wherein one end of the first resistance (Rg) is connected to the first source terminal and another end of the first resistance (Rg) is connected to the second gate terminal, and wherein one end of the second resistance (Rs) is connected to the first drain terminal and another end of the second resistance (Rs) is connected to the second gate terminal; the potential divider connecting an output of the first switching element to the second gate terminal of the second switching element such that a proportion of a drain-source voltage of the first switching element is configured to be provided as a gate voltage to the second gate terminal; wherein the energy storage device is arranged in parallel with the series connection of the switch and the sub-module resistor.