Band-gap transition induced by interlayer van der Waals interaction in MoS<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

We have investigated the electronic structures of single- and double-layered MoS${}_{2}$, composing of heterojunction structures such as graphene, MoS${}_{2}$, and SiO${}_{2}$ and MoS${}_{2}$ and SiO${}_{2}$, using scanning photoelectron microscopy. Negative shifts of both core levels and valence bands toward the Fermi energy have been observed. In connection with first-principles calculations, we have confirmed that the direct gap of single-layer MoS${}_{2}$ is changed to an indirect gap by stacking additional layers via van der Waals interlayer interactions.