In the present work, the channels of metallicity-sorted metallic single-walled carbon nanotubes (SWCNTs) have been filled with silver chloride. The data of high-resolution scanning transmission electron microscopy proved the filling of the nanotube channels and formation of few-atom-thick crystals of silver chloride. The electronic properties of the filled SWCNTs were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. Our results indicate the p-doping of nanotubes by silver chloride accompanied by the charge transfer from the nanotubes to the encapsulated compound and the downshift of the Fermi level by 0.36 eV. The calculated number of transferred electrons per nanotube carbon atom and the charge transfer density per nanotube length amounted to 0.0024 e(-) per carbon and 0.0406 e(-)/, respectively. It was found that the band gap opens up in the band structure of the filled SWCNTs resulting in their transition from metallic into a semiconducting state. This work reveals a direct influence of the incorporated silver chloride on the electronic properties of metallicity-sorted metallic SWCNTs and demonstrates the potential of precise Fermi level engineering of SWCNTs by filling their channels and achieving high doping levels, thus providing a platform for designing next-generation nanoelectronic devices.