We demonstrate a tunnel diode composed of a vertical MoS2/SiO2/Si heterostructure. A MoS2 flake consisting four areas of different thicknesses functions as a gate terminal of a silicon field-effect transistor. A thin gate oxide allows tunneling current to flow between the n-type MoS2 layers and p-type Si channel. The tunneling-current characteristics show multiple negative differential resistance features, which we interpret as an indication of different conduction-band alignments of the MoS2 layers of different thicknesses. The presented tunnel device can be also used as a hybrid-heterostructure device combining the advantages of two-dimensional materials with those of silicon transistors. (C) 2015 AIP Publishing LLC.