[en] A comparative simulation study on the band-to-band (BTB) tunneling current of van der Waals heterojunctions consisting of transition metal dichalcogenides has been performed using a method based on the non-equilibrium Green function combined with a tight-binding approximation. For a longer channel, a dip structure of low tunneling transmission appears on the transmission function from the source electrode to the drain electrode. This dip structure appears in the middle of the transport window and originates in the anti-crossing gap of the band-structure. It is found that the BTB tunneling current is strongly enhanced when a satellite valley (Q-valley) is located within the transport window. This enhancement is attributed to the Q-valley assisted BTB tunneling. (paper)