Integrated optics techniques have been used to form a three‐mirror laser diode configured to form a long active cavity and a short passive cavity. The third mirror results from an abrupt etched step down to the waveguide layer of a large optical cavity heterostructure laser. We have observed predominantly single‐frequency operation at current levels up to 1.5 times threshold. For certain ratios of passive‐to‐active cavity length, these devices operated multimode within a narrow frequency range, whereas diodes with different length ratios emit two modes widely separated in frequency.