A new type of transistor called "Static Induction Transistor (SIT)", by operation of majority carrier injection, has been successfully verified as a promising device for microwave high power operation. By using a novel structure and a process technique, the following remarkable results were obtained; (1) fmax of above 5 GHz, (2) amplifying power of 24 watts at 1 GHz, and (3) oscillating power of 100 watts at 200 MHz. The SIT showed a good linearity for power amplification and thermal stability for multi-chips operation.