A rearrangeable nonblocking silicon-on-insulator-based thermo-optic 4×4 switch matrix with spot size converters (SSCs) and a new driving circuit are designed and fabricated. The introduction of a spot size converter (SSC) has decreased the insertion loss to less than 10dB and the new driving circuit has improved the response speed to less than 1 μs. Supported in part by the National Key Basic Research Special Foundation of China under Grant No. G2000-03-66, and the National High Technology Program of China under Grant No. 2002AA312060, and the National Natural Science Foundation of China under Grant No. 60336010.