In order to realize a high performance switching transistor, a new trench isolated transistor with side-wall gates has been developed. In this transistor with a triple-gate structure, the side-wall of the trench is used as an extra-channel region. The new effects of trench isolated transistor with a triple-gate structure have been described. The advantages of this transistor are excellent cutoff characteristics, a small substrate bias effect and high reliability characteristics. It is found that the side-wall gate along the channel edge plays an important role for increasing the gate controllability and for decreasing the concentration of the electric field at the drain.