All‐guided wave interferometers using [3×3] directional couplers as beam splitters are analyzed in detail. The characteristics of such interferometers are compared with those of conventional interferometers using [2×2] beam splitters. It is shown that there are advantages in using [3×3] couplers instead of [2×2] couplers in the Mach‐Zehnder interferometric sensors and the Sagnac rotation sensors (gyroscopes).