The lack of a sizeable bandgap has so far prevented graphene from building effective electronic and optoelectronic devices despite its numerous exceptional properties. Intensive theoretical research reveals that a bandgap larger than 1 eV can only be achieved in sub-3 nm wide graphene nanoribbons (GNRs), but real fabrication of such ultra-narrow GNRs still remains a critical challenge. Herein, we demonstrate an approach for the synthesis of ultranarrow and photoluminescent semiconducting GNRs by longitudinally unzipping single-walled carbon nanotubes. Atomic force microscopy reveals the unzipping process and the resulting 2.2 nm wide GNRs are found to emit strong and sharp photoluminescence at ~685 nm, demonstrating a very desirable semiconducting nature. This bandgap of 1.8 eV is further confirmed by follow-up photoconductivity measurements, where a considerable photocurrent is generated as the excitation wavelength becomes shorter than 700 nm. More importantly, our fabricated GNR field-effect transistors (FETs), by employing the hexagonal boron nitride encapsulated heterostructure to achieve edge-bonded contacts, demonstrate a high current on/off ratios beyond 105, and carrier mobility of 840 cm2/Vs, approaching the theoretical scattering limit in semiconducting GNRs at room temperature. Especially, highly aligned GNR bundles with lengths up to a millimeter are also achieved by prepatterning a template, and the fabricated GNR bundle FETs show a high on/off ratio reaching 105, well-defined saturation currents and strong light-emitting properties. Therefore, GNRs produced by this method opens a door for promising applications in graphene-based electronics and optoelectronics.