Monolithic phase‐locked resonant arrays of antiguides, resonant optical‐waveguide (ROW) arrays, have been optimized for efficient in‐phase‐mode operation. Diffraction‐limited, in‐phase‐mode continuous‐wave (cw) operation is obtained from 20‐element uniform arrays to 250 mW output power, with (front facet) external differential quantum efficiencies of 41%. Single longitudinal mode operation is observed below 100 mW cw. In‐phase‐operating devices with and without Talbot‐type spatial filters are compared, and it is found that for ROW arrays Talbot‐type spatial filters are not required.