In face of the small-scale structure problems in the collisionless cold dark matter (DM) paradigm, a popular solution is to introduce a strong DM self-interaction which can be generated nonperturbatively by a MeV-scale light mediator. However, if such the mediator is unstable and decays into SM particles, the model is well constrained by the DM direct and indirect detection experiments. In this talk, I will introduce a model of a self-interacting fermionic DM, which is featured by a light stable scalar mediator. In this model, the DM relic abundance is dominated by the fermionic DM particle which is generated mainly via the freeze-out of itsannihilations to the stable mediator. Since this channel is invisible, the DM indirect detection constraints could be greatly relaxed. Furthermore, the direct detection signals are suppressed to the unobservable level since fermionic DM scatterings with a nucleon appear at one-loop level. By further studying the bounds from the CMB and BBN on the visible channels involving the dark sector, we show that there is a large parameter space which can generate appropriate DM self-interactions at dwarf galaxy scales, while compatible with other experimental constraints.