Geometries and energies if SinF- and SinF (n=1-7) were investigated with ab initio MO calculations; the Moller-Plesset perturbation and coupled cluster methods were used to take into account the electron correlation. The F atom is bound to the apex atom in the Si-n frame, and the electronic structures of the Si-n part in SinF- and SinF are similar to those of the corresponding Si-n and Si-n(+), respectively. The calculated electron affinities (EAs) of SinF are in agreement with the experimental values. The size dependence of EAs of SinF is similar to that of the ionization energies of Si-n at n greater than or equal to 5, whereas it is different at n less than or equal to 4. In the HOMO of SinF (n less than or equal to 4), the weak antibonding nature between F and Si greatly makes the Si,F-anions unstable, resulting in small EA. The vibrationally resolved photoelectron spectra (PES) of SinF-(n=1-3) were measured, and were completely reproduced theoretically.