molybdenum diselenide/tungsten diselenide (MoSe 2 /WSe 2 ), have been studied due to tunneling-mediated recombination and unconventional transport behaviors. [4,5] Main advantage of vdW heterostructures is that any of 2D materials can be arbitrarily stacked with weak vdW force without consideration of lattice mismatch, contrarily to the epitaxial growth in the conventional semiconductors. It has been well known that band structures of the TMDs depend on their thicknesses, e.g., lager band gap for thinner TMDs due to quantum confinement effect and homojunctions between the same TMDs with different thicknesses have unique band offsets. [6,7] Nevertheless, study on these homo-junctions are lacking. Just a few papers reported an electron transport in conduction band offset of the MoS 2 homojunctions. [8,9] However, MoS 2 shows only n-type electrical transport regardless of the thickness.Among the TMDs, WSe 2 has high tunability of charge carriers and high room temperature quantum yield, which is beneficial for optoelectronic applications. [10][11][12] It indicates that polarity of the intrinsically ambipolar WSe 2 can be easily modulated. Especially, as the thickness of WSe 2 increases, it shows carrier type transition from p-type to n-type due to a large shift of valence band and reduced contact barrier for hole. [13] Transition metal dichalcogenides (TMDs), one of the 2D semiconductors, such as molybdenum disulfide (MoS 2 ) and tungsten diselenide (WSe 2 ), exhibit novel physical and electronic properties that are useful for electronic and optoelectronic applications. Recently, the van der Waals heterostructures consisting of different 2D materials have been studied actively as various combinations of 2D materials can be fabricated with exceptional performance and physical properties. Nevertheless, study on homo-junction of the same TMDs layers is lacking. Here, it is demonstrated that a vertical homojunction consisting of two WSe 2 flakes with different thicknesses shows anti-ambipolar transport behavior due to a thickness-induced band offset at the interface. Photo-response current is generated by tunneling-mediated interlayer recombination at the WSe 2 homo-junction. The band structures of homo-junctions of TMDs can be engineered by the thickness, which would be beneficial for understanding transport at the interfaces of 2D materials and developing the next generation devices.