Abstract: Apparatus for opening and closing electrical circuits including one or more normally-open switches and normally-closed switches. A normally-open switch includes at least one MOSFET assembly consisting of a plurality of MOSFETs of different current-carrying capacities connected in parallel and circuitry for turning on the MOSFETs in time sequence. The normally-closed switch includes a pnp bipolar transistor, an npn bipolar transistor, and a circuit for short-circuiting the emitter-base junctions of the two transistors. The base and the collector of the npn transistor are connected respectively to the collector and the base of the pnp transistor. The normally-open and normally-closed switches both include a means for accommodating a current flow in either direction through the switch terminals.