A vacuum microdiode was fabricated with a silicon avalanche cathode and an on-chip microanode. The image reverse process followed by proper heat treatment was employed to form a photoresist sacrificial layer in shaping a microanode. The distance of approximately 3 mum between cathode and anode was achieved by adjusting the number of depositions of photoresist. On the top of the sacrificial layer, a multilayer (Al/TiW/Al) structure was deposited, which provided the microanode with good conductivity and mechanical strength. The dimension of the microanode was 8 (or 18) mum in width and more than 30 mum in length. The I-V characteristics of this vertical-type microdiode demonstrated the enhancement of current emission due to a strong electric field at relatively low anode voltages.