An apparatus (100; 200; 400) comprising: at least one semiconductor device ; a string of series-connected voltage clamp devices (110; 210) coupled in parallel with the at least one semiconductor device ; a bypass circuit (120; 220; THYR) configured to selectively bypass a subset of the string of series-connected voltage clamp devices (110; 210) to control a level at which a voltage across the at least one semiconductor device is clamped; and a control circuit (130; 230; 220') configured to cause the bypass circuit (120; 220; THYR) to shunt current through a first number of the series-connected voltage clamp devices (110; 210) in a first state and to shunt current through a second number of the series-connected voltage clamp devices (110; 210) in a second state responsive to the voltage across the at least one semiconductor device , characterized in that : the first state provides a clamping voltage greater than a maximum instantaneous voltage rating of the at least one semiconductor switch (10; 10a, 10a), wherein the second state provides a clamping voltage less than or equal to the maximum instantaneous voltage rating of the at least one semiconductor device , 2. and wherein the control circuit comprises: a string comprising at least one zener diode (D1, D2) and at least one resistor (R) coupled in series and having first and second terminals coupled to first and second terminals of the string of series-connected voltage clamp devices ; and a semiconductor switch (220, THYR) coupled in parallel with the subset of the string of series-connected voltage clamp devices and having a control terminal coupled to a terminal of the at least one resistor (R). at least one semiconductor device ; a string of series-connected voltage clamp devices (110; 210) coupled in parallel with the at least one semiconductor device ; a bypass circuit (120; 220; THYR) configured to selectively bypass a subset of the string of series-connected voltage clamp devices (110; 210) to control a level at which a voltage across the at least one semiconductor device is clamped; and a control circuit (130; 230; 220') configured to cause the bypass circuit (120; 220; THYR) to shunt current through a first number of the series-connected voltage clamp devices (110; 210) in a first state and to shunt current through a second number of the series-connected voltage clamp devices (110; 210) in a second state responsive to the voltage across the at least one semiconductor device , characterized in that : the first state provides a clamping voltage greater than a maximum instantaneous voltage rating of the at least one semiconductor switch (10; 10a, 10a), wherein the second state provides a clamping voltage less than or equal to the maximum instantaneous voltage rating of the at least one semiconductor device , 2. and wherein the control circuit comprises: a string comprising at least one zener diode (D1, D2) and at least one resistor (R) coupled in series and having first and second terminals coupled to first and second terminals of the string of series-connected voltage clamp devices ; and a semiconductor switch (220, THYR) coupled in parallel with the subset of the string of series-connected voltage clamp devices and having a control terminal coupled to a terminal of the at least one resistor (R). a string comprising at least one zener diode (D1, D2) and at least one resistor (R) coupled in series and having first and second terminals coupled to first and second terminals of the string of series-connected voltage clamp devices ; and a semiconductor switch (220, THYR) coupled in parallel with the subset of the string of series-connected voltage clamp devices and having a control terminal coupled to a terminal of the at least one resistor (R). <EOS>