Future expansion of computing capabilities relies on a reduction of energy consumption in silicon-based integrated circuits. A promising solution is to replace electrical wires with optical connections, for which a key component is a nanolaser that coherently emits into silicon-based waveguides to route information across a chip, in place of bulky off-chip devices. We report room temperature, sub-μm footprint, quantum-well-in-nanopillar lasers grown directly on silicon and silicon-on-insulator (SOI) substrates that emit within the silicon-transparent wavelength range under optical excitation. The laser wavelength is controlled by changing the InGaAs quantum well thickness and alloy composition, quite independent of lattice mismatch with the InP barrier, a unique property of the 3D core-shell growth mode. We achieve excellent luminescence yield and low continuous wave transparency power due to the well-passivated InGaAs/ InP interfaces. These sub-μm footprint long-wavelength lasers could enable optoelectronic integration and photon routing with silicon waveguides on the technologically relevant SOI platform.