The high performance of a resistive memory device based on electrochemical metallization is presented. With a solid electrolyte mixture consisting of zinc sulfide and silicon dioxide, the device combines the strengths of pure sulfide and pure oxide electrolytes, and exhibits various attractive characteristics such as forming-free switching, reasonably low currents, and high speed. Bipolar switching with an ON/OFF-state resistance ratio of about 100 is demonstrated by a direct-current quasi-static sweep. Pulse characterization shows that the device can be bistably SET and RESET using square pulses with pulsewidth down to 10 ns. Reliable endurance of 105 cycles and a stable retention time up to 106 s are also achieved.