A feasible method for integrating several silicon (Si) photonic devices with operating wavelengths separated by several hundred nanometers on a single chip will greatly help increasing capacities of small optical communication modules. This work demonstrates the integration of two photonic crystal nanocavity devices that exhibit ultrahigh quality factors (Q) and operate at the 1.31‐ and 1.55‐µm bands. A dual thickness Si‐on‐insulator substrate forms the base of the device. The two nanocavity patterns are defined by electron beam lithography on the thick and thin substrate regions and are transferred to the top Si layer by performing plasma etching only once. All dimensions of the fabricated 1.31‐µm nanocavity are ≈15.5% smaller (1–1.31/1.55) than those of the 1.55‐µm nanocavity; that is, they can be treated with the same photonic band diagram. Both nanocavities exhibit an ultrahigh Q > 2.0 × 106 and enable fabrication of nanocavity‐based Raman lasers for the 1.31/1.55‐µm bands with sub‐microwatt threshold.