For an optimal design of switching in power electronics a precise and reliable concept of protection against periodic and transient surge voltages is required. The characteristics of the most important active protective devices – d.s.a.s.-Si overvoltage suppressors, b.o.v. zinc-oxide varistors and b.o.d. breakover diodes – that are used for this purpose are compared here. Calculation and appliction examples are given to demonstrate that each of these three devices has its own application areas and that they complement each other so as to offer an economic and technically optimal surge-voltage protection in every case. Design fundamentals for determining losses and the cooling system sometimes required are presented.