A semiconductor switching string comprising a plurality of series-connected semiconductor switching elements (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N), each semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N including: first and second terminals between which current flows from the first terminal to the second terminal when the semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) is switched on; a third terminal to control the said current flowing from the first terminal to the second terminal ; and a local switching controller operatively connected with the third terminal to control a terminal voltage between the first and second terminals , such that the voltages applied to the semiconductor switching elements within the switching string are coordinated, the semiconductor switching string being characterised in that each local switching controller of each semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) being arranged in direct communication with at least each of its nearest neighbours in the semiconductor switching string and additionally arranged in indirect communication with the local switching controllers of a plurality of further semiconductor switching elements (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) via the or each said local switching controller of the or each said semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) with which it is arranged in direct communication, wherein the local switching controller of a respective semiconductor switching element arranged in direct communication with one or more other local switching controllers is configured to receive directly from the or each said other local switching controller a feedback signal corresponding to the terminal voltage of the semiconductor switching element of the or each said other local switching controller, each local switching controller being configured to vary during a switching transition the rate of change of terminal voltage of the semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) with which it is operatively connected, such that the degree to which each local switching controller varies the said rate of change of terminal voltage of the semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) with which it is operatively connected is influenced to a primary extent by the or each feedback signal corresponding to the terminal voltage of the or each semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) with which its associated semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) is arranged in direct communication, and to a secondary extent by the terminal voltage of each further semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) with which its associated semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) is arranged in indirect communication. first and second terminals between which current flows from the first terminal to the second terminal when the semiconductor switching element (12A, 12B, 12C, 12D, 12E, 12F, 12G, 12H, 12N-1, 12N) is switched on; a third terminal to control the said current flowing from the first terminal to the second terminal ; and a local switching controller operatively connected with the third terminal to control a terminal voltage between the first and second terminals , such that the voltages applied to the semiconductor switching elements within the switching string are coordinated, the semiconductor switching string being characterised in that <EOS>