Various important factors determining the snap-off time of the step-recovery-diode (SRD) are investigated. In addition, a new structure of SED is proposed, that is n+pp+ diode with abrupt n+p junction and narrow p base region. The analysis shows that because the carriers injected into the base region have larger diffusion coefficient, the snap-off time of such diode is greatly reduced. The process used to produce this diode is also described, and many diodes produced by this method have been employed in many practical circuits. The best result of the snap-off time is smaller than 50 ps (10-90%).