  In the quest to realize a scalable quantum network, semiconductor quantum
dots (QDs) offer distinct advantages including high single-photon efficiency
and indistinguishability, high repetition rate (tens of GHz with Purcell
enhancement), interconnectivity with spin qubits, and a scalable on-chip
platform. However, in the past two decades, the visibility of quantum
interference between independent QDs rarely went beyond the classical limit of
50$\%$ and the distances were limited from a few meters to kilometers. Here, we
report quantum interference between two single photons from independent QDs
separated by 302 km optical fiber. The single photons are generated from
resonantly driven single QDs deterministically coupled to microcavities.
Quantum frequency conversions are used to eliminate the QD inhomogeneity and
shift the emission wavelength to the telecommunication band. The observed
interference visibility is 0.67$\pm$0.02 (0.93$\pm$0.04) without (with)
temporal filtering. Feasible improvements can further extend the distance to
600 km. Our work represents a key step to long-distance solid-state quantum
networks.
