A newly developed hybrid-integrated Symmetric Mach-Zehnder (HI-SMZ) all-optical switch is reported. For integration, we chose the Symmetric Mach-Zehnder (SMZ) structure rather than the Polarization-Discriminating Symmetric Mach-Zehnder (PD-SMZ) structure which is similar to SMZ but more often used in experiments using discrete optical components. We discuss advantages and disadvantages of SMZ and PD-SMZ to show that SMZ is more suitable for integration. We also discuss about the use of SOAs as nonlinear elements for all-optical switches. We conclude that, although the ultrafast switching capability of SMZ is limited by the gain compression of SOAs, the very low switching energy is more important for practical devices. We then describe the HI-SMZ all-optical switch. This integration scheme has advantages which include low loss, low dispersion silica waveguides for high speed operation and ease in large scale integration of many SMZs with other optical, electrical, and opto-electrical devices. We show that a very high dynamic extinction ratio is possible with HI-SMZ. We also examine HI-SMZ with 1 ps pulses to show its ultrafast capability. Finally, we describe a 168 to 10.5 Gbps error-free demultiplexing experiment which is to our best knowledge the fastest experiment with an integrated device.